It depends on how long you're staying, and how comfortable you are charging on your credit card. If you're trying not to charge and only use the CC as a "fall back" option, then obviously you'll need more cash.
We are going in 2 weeks with DD5 and DS2 as well. We plan to charge any sit-down meals back on our debit card, and use cash only for minor purchases - snacks, small souvenirs, etc. Really we use our debit card for most things. So for us, about $50 - $75 / day is more than enough - last year we brought $600 for 7 days and had a lot of cash left over. If you want to use cash to pay for all of your meals, though, I'd definitely plan to bring more like $100 - $150 / day, depending on if you're doing counter service meals or sit-down meals.
Good luck deciding! Remember that there are many places around Disney to get more cash - they want you to be able to spend your money! And I'm never comfortable carrying around a wad of money, anyway, so as long as you have your ATM card, I would err on the side of a little less.