You guys are fortunate, being able to physically inspect your emooz.
Tame-Wild Emu Guy will have a wild guess:
to begin, it's far far easier to gauge the health of older emus. Here is one of my favourite photos, of Uno Chick. This is what a healthy yearling looks like:
I'd be looking for spriteliness. For example, if a chick were sitting while the others were milling around eating, I'd assume it was ill. Emooz love to rest after a good meal, but if if a clutch is grazing, and one bird were sitting (listlessly), that'd be a bad sign.
Bear in mind that I observe clutches of incubated-in-the-wild chicks. Over the first year or 18 months, you look to see if there's an alpha and a runt -- again, not evident in your chicks yet, but it's something to watch for. If one gets runty, you can cheat when you feed them. The motto here is: 'No one gets left behind.' The runt will be at the back, so you sling handfuls of extras at its feet.
Check them for actual physical deformity. One of the 'original' birds here had been under my observation for five years on the day a mate of mine, a horse breeder, turned up. Took her three seconds to note that 'Number One' has a slight bow in one leg.
Finally, I'd expect chicks at this age to be moving around pretty homogenously. If one chick -- can you identifty them yet? -- were persistently at the back, or left behind, I'd note that.
Supreme Emu, Western Australia
[Got Uno Chick here this morning, being auntie to the very last orphan of Eric's clutch. And a wild bird that maaaay be Uno's first every consort. Felicity was here two days ago with her potential consort, 'Groestl the Emu.']
P.s.: you'll soon get to watch them become black heads. I love the black-head stage: at about one season, you'll see the very first tiny 'break' in their baby plumage. It'll be on their necks, and they'll simultaneously get their first tiny fuzzy toosh feathers appearing.