At this age, mother does not sit on them. They are feathered enough to keep themselves warm. This confuses many observers because the mother is sitting on them one day, then the next, she is absent.
If this happens, watch for an hour at a respectful distance, without looking away. No phone breaks, no coffee breaks, just staring at the nest. She returns and feeds quickly, it takes less than 10 seconds, so if you look away, you will miss her. Once you see that she has returned, please leave them alone. Mothers have been known to abandon a nest when people keep looking at it and taking pictures. These are wild birds and their privacy should be respected.