Our situations are very different as I have an only child. But I have been a SAHM since she was born. When she started full-day kindergarten 2 years ago, I didn't know what I was going to do with myself. (Never mind that sending my precious 5-year-old off to full-day school was heart-wrenching, and it was January that year before I stopped feeling a lump in my throat as I watched her walk thru the school doors!)
Anyway, I've been pleasantly surprised to find out that there is LOTS to keep me busy day to day during the school year related to "homemaking." In fact, I've come to enjoy planning out my work schedule for the day without having to consider feeding times and entertainment for my dear daughter. Also, there have been multiple school volunteering opportunities I've been able to freely participate in.
I also noticed, at least with an elementary age child, how inconvenient it would be to have a job, but then have to be there for your child on sick days, snow days, early closings, late openings, etc. I'd much rather "be there" for my child.
Speaking of being there, I don't think enough is said of the benefits for child when Mom is simply available. Drop-off, pick-up, help with homework. Hugs after school. Maybe I'm a sap, but I think it's good for my daughter right now, and I'm grateful that our home situation allows it. Not all moms are fortunate enough to choose to be SAHM.