I would keep him on the same diet for a few months while he gets settled in. Keeping him on the same diet may help the transition since he's going into a new home with new people, but his food is familiar to him. Fruits and veggies are always good to feed your bird, so I would keep him eating those while he's young and willing to try new things. Also, pellets are good to introduce young. You might have to try a few different brands and do your research on which one you see is good for your bird. My theory is any pellet your bird will eat is a good pellet. Pellets along with fruit and veggies and some sprouts is a good, well balanced diet. Most birds like nutriberries and they are a great pellet food. Main thing is to make sure they're getting enough water and food the first few days, so I'd feed whatever he'll eat the first week or so, so he doesn't lose weight.
I hope this helps!!