They love smashed, boiled eggs and yogurt. I mix both with a little of their starter crumbles and let them have at it. If you've never given them treats before, don't be surprised if they act as though you've thrown a rattlesnake in with them!
Worms, they like bread especially wheat crusts, watermellon rind, anything as long it is not poisionous or over salty. Mine would go nuts for the baby spiders in the spring. Just be sure to feed them some parakeet grit with their treats, I would sprinkle it on like salt. It is sure fun to watch them with worms, you could put a hundreds worms in with them and the first worm grabbed, all of the others swear it is the last worm and chase after the lucky bird, it is a riot.