A few things to notice here:
The largest chick (on the left) is starting to get out of the nest cup. The smallest chicks are almost under it.
At least some of the chicks are now opening their eyes and when the largest chick spreads its wings you get a really clear view of how the feathers grow in an outer sheath making them look very separated. Eventually this will be shed as the feather develops fully.
The advantage of being able to get out of the cup becomes clear when the parent arrives.