I tried to have 2-3 foods for my young chams. I'd highly recommend black soldier fly larva (probably smalls or medium for a 3 month old)... my guys would eat several of them each day plus their crickets. They're easy to feed and high enough in calcium that you don't need to dust them. My guys love them, too! You could try micro/small superworms, as well. They are cheap and have a really long shelf life, but its recommended they not make up more than 20% of their diet. I also gave them a SMALL hornworm now and then, but it was hard to find them small enough at that age, and they grow so quickly they're not worth buying until they're older.
Based on my experience with 2 young vieleds, and what I've learned along the way, I'd recommend the following...
- order your feeders online. Even with shipping charges, it is far less expensive then the pet store, much better quality, and wider selection. (I really like rainbowmealworms.com for my staple feeders, although I am now raising my own)
- I would make my staple feeder a rotation of: small crickets, small dubia roaches, black soldier fly larva, micro/small superworms in that order. The only one I would limit would be superworms (use them as desert).
- I wouldn't waste my time buying small hornworms unless you have multiple chams where you can feed them off in a day or two.
-If you are up for raising your own, silkworms have been easy for us and would be great to throw into the rotation!
- don't waste your time on wax worms or butter worms yet, or at all.