ChickenTumble, you need advice from folks with emu chicks that they hatched. I am the sole Wild Emu Guy on BYC -- I observe wild emus here in Western Australia.
So I know nothing about the likes of rabbit food and chick starter. Hang out here, and you'll hopefully get insights from more knowledgeable members.
However, I can add comment: variety is good. Fresh is good. If you can, chop fine a little of every fresh fruit and vegetable you have. The rule for emus is simple: if Yummy for Emus, they'll scoff it up.
They love all sorts of fruits -- except citrus -- whether fresh or dried. They like chopped spinach and kale, I hear from U.S. folks.
Here's an interim equation for you: for certainly two or three weeks, they will be well fed if they are getting any sort of medley of store-bought and fresh-chopped and dried fruits and vegs.
If there are grass and flowers on bushes or such like outdoors near them, try them out on that!
Mine are never given junk food of any sort. But they sometimes win at the game of Eat Supreme Emu's Breakfast, and get bits of wholemeal bread and broccholi and pasta and rice -- note the types of grains. They love grains. That is, we know they'll scoff down a very wide range of 'people food.'
