Here is a good place to start
http://ball-pythons.net/forums/showthread.php?p=1410665

My daughter worked me for a snake for years. She got her first one at age 6, btw, she spent her OWN money for it. We now have (which she handles all of) balls, and boas. A lot depends on how your children are with animals, as far as respectful and understanding, and being careful with them. Most balls have great tempermants. However, they are all individual, and can be crabby too. My daughter knows, that if for some reason one of the snakes bites her, she is NOT to drop or throw it. It won't hurt her. And she has no fear of them, helps clean them, and helps feed them. If you know your kids, and get to know your snakes personality, it can be a great experience for them. They are great pets.

Short answer, if proper care and education is taken, no, 4 & 6 isn't to young.

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