Hm. Now might be the time for a good ol' responsibility lesson. :D

What about starting with a fish. Say, a betta, since they're hearty and easy to take care of. If Charlie takes really good care of the feeshie, then he can get a dog.

Bettas require a pinch of food a day, they can live in a small bowl with no special equipment (just as long as said bowl is kept in a warm place), and what's more: they're cheap. And they don't bark and need to be walked. (But put a mirror in front of their bowl and watch them attack it with fins flared! So amusing. Funny, aggressive fish.)