A child can usually testify by the age of 12, but it can be earlier if they understand the difference between tellilng the truth and a lie. Its up to each trial judge to make a determination of their own as to how mature and understanding each child is about that issue and whether to allow them to be sworn to testify or to allow them to testify without being sworn, or not at all.
It is up to the court (the specific judge) and any applicable rules. The child may be asked to testify in camera (in the judges chambers) or in open court. Usually it is determined based on the age, maturity, and understanding of the child. Whether or not the child understands the difference between the truth and a lie. Some courts (not all) will allow a child to testify and not have the testimony be "sworn" if the circumstances require. Check with your attorney for specifics. Good luck.
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