For me the treats started quite by accident. A few days after getting some 1-week-old chicks, I noticed that my Basil was being attacked by something. DD and I discovered it was covered in little brown beetles. We picked off every one we could find, putting them in a jar as we went. Dumped them into the brooder and the chicks huddled in the back for a second, scared of them. But as the beetles started crawling around, something triggered in their little brains and one of the braver ones ran over and grabbed it in her mouth. Then the fun started. She had never had food move before, so when she felt the beetle wriggling in her beak, she gave a squawk of surprise and started running in circles. The second chick to grab a beetle reacted exactly the same way. But after that it was a feeding frenzy and there were excited little squawks of "I got one, I got one" every time they found one in the pine shavings. They would then desperately try to find a private corner in which to consume it while the rest of them gave chase.
Since then, we regularly peruse our vegie garden and have found a variety of caterpillars and beetles eating our food. They are meticulously removed from the plants by hand and when done, we take them into the backyard (chicks have been outside now for 3 weeks or so), and at the sight of an outstretched hand, they all come pelting across the yard to see what we've found for them this time.