I was in a similar position a little over a year ago - my daughters were a little older than your boys, my youngest was 8 months and i was still breastfeeding. I could pick my own hours, my own days, as long as some of the work was done....like you, we didnt really need the money, DH works two jobs and i love staying at home.... but hey any money is good money.....my mum, my MIL, and my sisters (when they had RDO's) looked after my girls - 4 hours a day for 3 days.....
It worked. Life was busy, running here and there dropping them off, picking them up. I enjoyed the work....but i only lasted 3 months....fell pregnant with #3 and now i will happily stay at home till my youngest turns 5 (around 2012 !!)...
Bottom line is, i think if you didnt take this opportunity, you may lie awake for a long while yet, wondering what you let pass.....try it, so what if it doesnt work, you can proudly say 'nope, that wasnt for me'......you may love the 12 hours you get to yourself.....i dunno, i reckon its worth a try, even if you give it 3 months.....if you hate it, leave. Whats 3 months out of your life really ?????