As everyone else has already said, change is stressful for chickens but they'll adapt in time.
Dried meal worms are an excellent treat (and full of protein) and unlike the other greeter, my girls love banana. Here's a chart showing some other healthy snacks:
Just remember to keep the snacks to no more than 10% of their daily diet so they eat their nutritious feed.
Have fun and if you have questions, feel free to ask!