Can the child change her answer before the examiner moves on to the next question?

Whether the child can change his or her answer is decided by the proctor on a case by case basis.  Generally, the proctor will allow the child to change answers if they do so before moving on to another question.  Most proctors are very flexible and care about making sure the child gives their best answer, but they do try to prevent the child from second guessing herself too much and make sure that the test is done in a timely manner.