The defendant was convicted of second degree assault, RSA 681:2, after a jury trial. On appeal, he claims that the *48Superior Court (Nadeau, J.) abused its discretion in finding the four-year-old victim competent to testify and in denying the defendant’s motion for a new trial on the ground of newly discovered evidence. For the reasons that follow, we affirm.
Shane Kelley is the child of Jerry Kelley and Barbara Mills, who are divorced. Barbara Mills is the wife of the defendant. In January 1989, Shane was three years old and living with his mother and the defendant; he visited his father’s home on alternate weekends.
At 6:00 p.m. on Friday, January 13,1989, Shane’s father and stepmother Tess arrived at the defendant’s home to pick up Shane for the weekend. Two hours later, while she was bathing Shane, Tess noticed severe bruising on him. Shane told her that the defendant had spanked him for not remembering the color blue and refusing to stay in the corner. After telephoning Barbara Mills, who hung up on her, Tess called the police, who advised her to come to the station immediately.
Jerry and Tess Kelley brought Shane to the police station, and the three were then taken by the police to the hospital emergency room, arriving at approximately 9:30 p.m. Dr. Tim Donnelly, the attending physician, examined Shane and found extensive bruising on his buttocks, legs, arms, and back. Photographs were taken of the bruises. Because of the pattern and degree of bruising, Dr. Donnelly suspected child abuse. Speaking with Dr. Donnelly independently from his father and stepmother, Shane stated that the defendant had caused the injuries with his hand. In the doctor’s opinion, from the appearance of the bruises, they could not have been sustained within three or four hours but were probably over six hours old and likely between twelve and twenty-four hours old.
On the day in question, Shane had been at a babysitter’s from 6:30 a.m. to 5:00 p.m. At the defendant’s trial, the babysitter testified that she never spanked Shane. She had noticed bruises on his thighs that morning, as well as what appeared to be a rash on his buttocks. Dr. Donnelly had testified that in the immediate period after injury, the reddened area could be confused with a rash.
The defendant testified that he had been home with Shane after 5:00 p.m. the previous night and admitted having spanked Shane in the past, but he denied spanking him on January 12 or 13. Shane testified that the defendant had spanked him at the defendant’s house and identified the photographs of his bruises. According to Shane, he was spanked because he “didn’t remember about the blue.”
*49Prior to trial, a hearing was conducted to determine whether Shane, then four years old, was competent to testify. After brief initial questioning by the prosecutor, the trial judge engaged in a lengthy colloquy with the child. The judge concluded that Shane was competent to testify based on his ability to observe and narrate “as well as any four-year-old” and on Shane’s statement that “he wants to tell the truth.” Defense counsel objected, stating that “when [the court] asked [Shane] if he knew what would happen to him if he didn’t tell the truth or it was important for him to tell the truth, I don’t think he showed a clear understanding of the importance between telling the truth and not telling the truth.” The judge responded that he thought that “for a four-year-old he’s demonstrated that he—it’s important to tell the truth.” In his charge to the jury, the trial judge instructed the jurors to “apply particular caution” in evaluating the testimony of a child. The defendant argues that the trial judge erred in (1) finding that Shane understood the obligation to tell the truth; (2) finding that he demonstrated an ability to remember and narrate events; and (3) failing to determine whether Shane could distinguish between truth and falsehood. The defendant below, however, objected to the competency determination solely on the first ground asserted here, i.e., that the witness had not demonstrated an understanding of the obligation to testify truthfully. Accordingly, the other grounds not having been properly preserved, they will not be considered on appeal. State v. McAdams, 134 N.H. 445, 447, 594 A.2d 1273, 1273 (1991).
Whether a witness is competent to testify is a question of law for the trial court. State v. Blum, 132 N.H. 396, 399, 566 A.2d 1131, 1132 (1989). New Hampshire Rule of Evidence 601 sets forth the law governing competency:
“(a) General rule of competency. Every person is competent to be a witness except as otherwise provided by statute or in these rules.
(b) Incompetence of a witness. A person is not competent to testify as a witness if the court finds that the witness lacks sufficient capacity to observe, remember and narrate as well as understand the duty to tell the truth.”
The import of Rule 601(a) is to establish a presumption of witness competency that may be overcome “by statute or [other] rules,” id., or by findings pursuant to Rule 601(b). State v. Aikens, 135 N.H. 569, 571, 607 A.2d 948, 949 (1992). “Absent an abuse of discretion, this *50court, which must act on a cold record, will not disturb the trial court’s determination of competency when there is evidence to support it.” State v. Scarlett, 121 N.H. 37, 39, 426 A.2d 25, 27 (1981).
As for the trial court’s finding that Shane understood the obligation to tell the truth, the record shows that the judge first ascertained from the witness that the prosecutor had spoken with him on the subject. A colloquy then occurred, during which Shane stated that he wanted to tell the truth and acknowledged that his parents would be upset if he did not tell the truth. In ruling Shane competent to testify, the trial court was impressed that “[h]e said he wants to tell the truth, he obviously is able to observe and understand things.” These findings were made after an extensive examination on subjects of interest to a four-year-old (e.g., his favorite cartoon character, the circus, playing with his friend), and relating to his observations of the bench and the judge (e.g., “How come you got that dress thing on?”). That Shane’s answers came primarily in response to leading questions is not problematic, as such an approach is neither out of the ordinary nor impermissible where the witness is a young child. See N.H. R. Ev. 611 (reporter’s notes) (discretion to permit leading questions on direct examination “when the witness is very young”).
Nor is it significant that Shane did not utter any particular “magic words” indicating comprehension of the obligation to testify truthfully. In re Gerald, 471 A.2d 219, 221 (R.I.1984). What is significant is the trial judge’s overall firsthand impressions of Shane’s responsiveness and desire to be truthful. Id. “[B]ecause so much depends upon his observation of the witness,” State v. Pettis, 488 A.2d 704, 706 (R.I.1985), the trial court’s conclusion that Shane was competent is entitled to great deference. The question is not whether we would have ruled as the trial court did, but whether there is sufficient evidence in the record to ground the finding. Our review of the record reveals sufficient support for the trial court’s determination of competency. We find no abuse of discretion.
The defendant’s second contention on appeal is that he is entitled to a new trial based on newly discovered evidence; namely, the purported post-trial recantation by the victim of his accusation against the defendant. At a hearing on the defendant’s motion for a new trial, Barbara Mills testified that she asked her son Shane, several months after her husband was convicted, if the defendant had really hit him. He said “no,” according to her testimony, and stated that he had told the judge the defendant had hit him because his father had promised *51him a toy jeep if he told the truth. Shane told her that his father had told him that “the truth” was that the defendant had hit him. Shane’s mother further testified that Shane had told her that it was his father who had hit him. She admitted that, at the time Shane made the statement, she and Shane’s father were embroiled in an ongoing custody dispute. Shane, although available, did not testify at the hearing.
Recanted testimony is a species of newly discovered evidence for purposes of a new trial motion. See 58 Am. Jur. 2d New Trial § 440 (1989). In order to prevail on a motion for a new trial on the ground of newly discovered evidence, the moving party must show
“(1) that [he] was not at fault for not discovering the evidence at the former trial; (2) that the evidence is admissible, material to the merits, and not cumulative; and (3) that [the evidence is] of such a character that a different result will probably be reached upon another trial.”
State v. Abbott, 127 N.H. 444, 450, 503 A.2d 791, 795 (1985) (citations and quotations omitted). When the purported new evidence is a recantation by a prosecution witness, the third prong of this test will not be met if the trial judge finds as a threshold matter that the recantation is not credible. See People v. Minnick, 214 Cal. App. 3d 1478, 1482, 263 Cal. Rptr. 316, 318 (1989) (in deciding motion for new trial based upon recantation, trial judge determines whether new evidence credible, then whether different result on retrial probable). Whether to grant a motion for a new trial is a question of fact for the trial judge, whose decision will not be overturned unless it is clearly unreasonable. Abbott, 127 N.H. at 450, 503 A.2d at 795.
After hearing all the new evidence, including a tape-recorded interview of the child in which Shane stated that the defendant did not hurt him, the trial court concluded that the evidence was not “of such a character that a different result will probably be reached upon another trial.” Noting that Shane’s post-trial statements and those of the witnesses who reported them “must be viewed in the context of the bitter custody and marital dispute which is taking place,” the court found them lacking in credibility. “We will not overturn the credibility ruling of the factfinder, who is in the best position to make such a determination ....” State v. Chase, 135 N.H. 209, 215, 600 A.2d 931, 935 (1991). Having upheld the trial court’s finding that the new evidence was not credible, we will not address *52the defendant’s argument that part I, article 15 of the State Constitution ought to guarantee him a new trial where he produces credible new evidence of recantation. After reviewing the record, we are convinced that the trial court’s decision to deny the motion for a new trial was not clearly unreasonable.
Affirmed.
Brock, C.J., and Johnson, J., dissented; the others concurred.