I know it's already been said, but I have to re-iterate: Don't use sand with cresties. It's a bad idea, and they don't live in sandy places in the wild.

Bed-a-beast is a good choice, as already said, if you absolutely must use a natural substrate. I personally use paper towels though.

The big issue with ingesting substrate really only is eating. If you don't feed crickets on the substrate you don't have much to worry about. Still though, for anything under 6 months of age, you might as well go ahead and have them housed on paper towels, save the natural bedding for your large juvie/adult crestie homes!