When you get the rentals go ahead and get poles also so that if your nephew is a good athlete he can have them right from the start. The no poles for kids thing is a completely stupid American teaching thing designed more to make the instructors life easier than as a real benefit for the kid.
You might think about poles for children this way.
Five to six never evers, five to seven years old, all learning to ride a chair. Probably a few are little too short to land square on the chair seat, an adult helper or two from the lift line to help a few of them, and you. Now, is there a safety lesson in this somewhere? Are the poles so important to their skiing development the munchkins need to worry about themselves, the chair, the new adult they just met, where is mom and dad and my brothers and sisters, I am hungry, I am scared, and will the poles get in the way and trip them out of the chair, be dropped and when they bend over to pick them up the chair bonks them in the head! I guess that is enough to think about on the safety issue. This is not an American issue by any means; it is a SAFETY issue with some children, sometimes; agreed to by munchkin ski instructors around the world.