if thats with tail than prob, tiny crickets, and maybe ever fruit fly's still. feeders should be no bigger than the width of their mouth and they can be givin as much as they will eat at that age.
here is a blog with some great info by another member https://www.chameleonforums.com/blo...-keepers-young-veiled-panther-chameleons.html
If it's 3-4 months old and is only 3-4 inches from the tip of the snout to the TIP of it's tail you should not buy him/her. That chameleon sounds severly undersized for it's age and is probably very unhealthy or isn't being cared for properly. If it's 3-4 inches from the tip of the snout to the BASE of the tail than it is normal sizedand sounds good. If you want to get a great healthy veild you should look into buying from one of the chameleonforums site sponsers. The site's sponsers will be able to provide you with a much healthier chameleon and provide you with much more accurate customer service if you have any questions than compared to most pet stores. Plus if you end up purchasing a sick neglected chameleon from a chain pet store or something you will be giving money to and supporting the people that routinley neglect and torture chameleons(sorry, I'm a little passionate about that issue). It may be a little more expensive at first to buy from a CF sponser, but the quality of chameleon and the fact that you won't have to spend a ton of money at the vet will be worth it. Good luck and hope you find a happy and healthy cham!
-Alex