When I first started looking into breeding, I asked the same question and most people told me to start with co-doms and dominant.... Things like pastels, spiders, pinstripes, fires, etc...I think they all produce some good looking offspring.
Personally, I think it's awesome that you're allowing your son to do this so early. I didn't have an interest in snakes until I was almost 21 years old and I've been constantly fighting my parents along the way. I recently had to move back in with my parents upon graduating college, and I'm fighting with my mom weekly about my snakes.... Dad is cool with it... even though he's terrified of snakes... I really wish i would have had an earlier experience with them.
By the way, not sure how much you guys have been looking into ball python morphs... but I'm a huge fan of: www.worldofballpythons.com .... great website. 
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Teresa
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3.0 Dogs (2.0 Chihuahuas, 1.0 Toy Poodle)
1.5 Cats
1.0 Cockatiel
1.0 Indonesian Blue tongue skink
Ball Pythons
0.1 100% Het Albino (Watson)
1.0 Pastel (Sweets)
0.1 Spider (Daisy)
1.0 Albino (Gormagon)
1.0 Lesser (Wendell)