Can anyone tell me what can cause a child's toe to overlap?

Genetics, injury.: An overlapping toe in a child is usually genetic, if there is no history of injury. You should take your child to a podiatrist for an evaluation. He/she may order x-rays to determine the cause. In most cases, if there is no pain, no treatment is necessary.

Starts in womb: This often originates from crowding in the womb, where the walls push against the outer toes and they assume whatever position they can. Since human babies don't get up on their feet to push them back into place until about a year, the issue may persist.