Nice and what a very generous uncle you are. He may not be aware of what bitcoin is today but after the right time, he'll value it more than what he has soon.
P.S. To avoid losing this btc, you should create kinda back-up procedure.
Yes, although you have given it to your nephew still create a back up for yourself so if ever it was accidentally lost you can recover it easily with your back up.
Execute what you are thinking, everyone's agreeing with you.
That's nice of you being an uncle but I don't think if that would be a great idea since you have mentioned that your nephew is just 4 yrs old. Well giving it to him is a good thing but how can he evenre make it grow? You have a great idea but it's complicated it your case especially your nephew is not yet aware of the systemtime. My advice for you is to make it grow first then give him some soon.