I'm not really a full time SAHM anymore, but when I was I used to keep rather busy. I did go out a lot though, and my kids did a few activities which took up a big chunk of the day. We used to bake a lot (because I am a sweet tooth.) And I would do things I enjoyed during the day while they played like lie outside reading a book. I came on here a bit during the day as well! I went through a phase of making juice every day for morning tea and I'd make myself a really nice lunch and sit outside with the kids to eat it. I probably used to spend a couple of hours on the phone most days. I'd take the dogs for a walk most afternoons. My life is in a mess at the moment but I'd like to settle down into some kind of routine again.
If you are really finding it boring could you study or something? Or concentrate on something for YOU once the housework is all done?