The best diet for ANY animal (people included) is a varied one. While you can usually get away without crickets, it's still best if they get a nice variety.
Mealworms I would generally stay away from -- I use them mostly for carnivorous arachnids, but not for any of the reptiles. The exoskeleton causing impaction is one reason, the other being that, if not chewed before being swallowed, they can and will live long enough in the stomach to eat through it, killing the animal slowly and painfully. Kingworms and superworms are great staples, to be supplemented with hornworms, silkworms, butter worms, phoenix worms, maggots and the occasional wax worm. Don't forget the calcium supplements! Very important.
Cresties also need a variety of fruit and vegetables in their diet, and tend to eat well on baby food.
Crested, fat tails and leopard geckos are all nocturnal and do not need UVB lighting, but fat tails and leos need heat. A UTH generally works for most setups.
Stay away from sand for babies and juveniles -- this can also cause impaction and kill them.
African Fat Tail and crested geckos are a little more needy than leos as far as humidity, and AFTS tend to be not quite as nice.
One of the most important things to know is that your child can grow tired of the pet. A friend of mine has a leopard gecko named libby who is now 22 years old -- please be prepared to care for it this long before getting if for children, because if they DO tire of it the animal is just going to be passed from home to home to home. Not fair for the lizard. They get issues just like any pet.
Buying from breeders is very much the best way to go.
http://www.theurbangecko.com/index.html[/url]
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http://www.okanagangeckos.freeservers.com/
http://www.mountaingeckos.freeservers.com/
http://leopardgecko.com/
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BUYER BEWARE on faunaclassifieds.... make sure to utilize the Canadian Board of Inquiry for anyone you are thinking of buying from. Either search the sellers name, or post a new inquiry. Just like any classifieds section, there are bound to be a few "bad seeds". Most of the stuff I hear of are good transactions, though.
http://www.faunaclassifieds.com/foru...play.php?f=486