M.J.
Most of my friends have gone back to work when the kids entered school. It's not necessarily easy to return to work, but the kids are gone for a long stretch of time and they got bored at home.
Your kids will need you less when they're in school. The fact is, they're away from you longer. Even working parents are able to get time off for field trips sometimes (and schools aren't doing as many anymore due to budget cuts). Picking kids up from school is overrated -- let me tell you, I would gladly avoid our school parking lot (aka Darwinland -- survival of the fittest there ... scary!). I work part-time and pick up our son after school and it's no picnic.
As far as childcare, many schools offer before and after school care on-site and districts provide summer programs, too. Our son is currently in our district's summer program part-time while I work. Many daycare centers and private schools also will offer fun summer programs for school-aged kids.
I'd say pursue your dreams. My mom went back for her master's when we were in school and launched her dream career. The extra income allowed my parents to retire early. She really enjoyed those years working and I honestly think she was happier then than when she was home with us kids.