The thing I miss most: silence
I don't mean that in a depressing way because I love my kids more than anything. But man, I miss just sitting in my car with nobody talking to me for like 20 minutes. Or being able to watch a movie without pausing it 47 times. Used to take 2 hour runs on Sundays with my headphones. Now I'm lucky if I get to pee alone. Sometimes I sit in the garage for an extra 5 minutes just to not hear anyone ask me something.
Headphones saved my life when the kids were younger. Even just putting them on for a podcast or music while doing laundry made a difference. You don't have to actually play anything sometimes.