Hi there! Welcome to IIS!
You've made the right decision by seeking advice first, and not just getting him a cheap ebay refractor, which ultimately he would be disappointed with.
The best scope for a child would have to be a 6" or 8" dob. They're easy to use, easy to setup, require no batteries or power to use, and are great value for money.
Check out shops like Bintel, MyAstroShop and Andrews Communications, who all sell versions of the 6" and 8" dobs.
An example one is here:
6" dob at MyAstroShop
Make sure you keep asking questions!