Why would you want to?! You shouldn’t put your 10 year old child in that position.
Most of the time, children are not called into court as witness or to observe. If they are needed to be questioned, I do not think that it would happen in open court and it would only be for the most unusual reasons.
As jillb questioned though, why would you want to put a child in that position? Regardless of what your ex has done or does, that is this child’s parent and they will NOT understand that you are protecting them or doing what you feel is right. They will continue to love both parents and putting them in the position of testifying will, in their mind make whatever happens their fault.
I think it would be at the discretion of the presiding judge, on whether he wanted to hear the child’s testimony at all, and whether it would be in chambers or open court.
It would depend vastly on what the issue at hand was, and whether the substance of their testimony could be obtained by other means.
May I call my daughter as a witness? She is 10.