They make a lot of good bows that are adjustable these days. If he's only 5 I'd suggest something very inexpensive to start out with.....a fiberglass bear recurve will get him going.....make sure he has a glove for his fingers and an arm guard....let me know I have a few kids gloves kicking around if you want one.
Genesis bows are OK, but they have no letoff, there are better kids bows out there now.....
If you want to take the plunge and spend some money, right now...he's probably not even at 18 inch draw length....so even the following kids bows might be too big.....
Diamond Edge goes from 18-28" draw length but weight is only in ten pound increments. (ie you'll need to change out the limbs as he grows)
I think the Mission Maniac (low grade Mathews) is another very adjustable bow, I think even the draw weight very adjustable (something not seen in most kids bows of past) This is definately one to look at.
Wal mart sells carbon arrows for 30# bows this will be fine for him.
Since you have little experience in archery you should probably see a pro shop.......make sure you get something that can grow with him. To fit him properly they will measure his Draw length, and get an idea what poundage he can pull. Average 5 year old probably has a 16" DL and can pull 20 pounds.....