A child is a competent witness. Only rider is that the child should be able to give rational answers to the questions put.
When a party wants the court to record evidence of the child witness , it should be examined in chief in court and also cross- examined by the other side. Without giving opportunity to the other side to cross-examine , court cannot consider that evidence. So even child , if a witness has to be cross-examined in court. If it is civil case , before a commissioner appointed.