Your nest box is only going to get nasty in coming days with lot more poops, it is a common stuff when babies are around. You can consider changing it now because soon flies will infest, so do roaches and other unwamted guests.
It has been a long time since I had my birds....but I remember the babies will
poop as far out of the nest as they are able. It looks like your babies cannot
scoot far enough because of the crate...so they poop too close to where they
have to sit. Would a nesting bowl be better? I used pine needles and let the
birds build their own rather large nests in a large nesting box/cubicle...and the
poop did not seem to get as nasty as in this photo.