Why do you feel the need to do so many extra-curricular activities related to child education? Can't you take your kids to the park, show them stuff and talk to them about it? One of the cool things that most adults forget about childhood is that everything is new for kids. Even stuff that kids are used to; they have really only scratched the surface of- they haven't had the time or the life experience to deeply understand things, but they also haven't had the life experience to become jaded or cynical. Spending some time around them doing stuff that is not homework, can be fun, or at least interesting.
Do you want to be unfulfilled?
If you truly cannot find joy in anything, then you are likely suffering from depression, and you should go see a doctor. It won't get better by itself.