One of the great joys for me is watching my kids when they don't know I'm watching.
When they are sleeping is one, but when I get to see their personalities come through...that's great.
Sometimes I'll catch them when they are playing together at home or with a play date, but usually, it is through the window of the classroom at nursery school.
Peeking in on their lives as they develop, oblivious to my observation (hopefully no observer effect here, see Decoding the Universe did teach me something) is just a pure joy.
Makes the sleepless nights worth it....uh, kind of.