We were discussing on the live stream whether Leo is the youngest. The question came up whether yellow feet (Leo) was the last to develop a mask.
I buzzed through some photos I had saved...I'd say yellow feet (Leo) has more of a mask in this one than the girl in back with her mouth open.

And this one 2 days later I would say the youngest is the girl in front of Leo, both by mask and wing feather length.

Based on current fluff loss/feather development I think the youngest is Aria. My personal suspicion is Matilda is the eldest, Leo & Lilac are a toss up-they hatched a few hours apart, then Aria.
Yes, I agree. Aria was also smaller than the other 2 females in these pictures -- about the same size as Leo.
It's too bad that Leo is not the youngest. It would have lessened the chance that an unready female will fledge too early in order to join her siblings..