My mom's friend quit her job a few months ago to be at home and do volunteer work. She has two adult kids who are out of the house, and two teenagers still living there. Like your kids, hers are mostly self sufficient, so they don't really "need" her at home, but she quit because she didn't like her job and they didn't need the money.
One of her kids has Down Syndrome, so a lot of her volunteer work has been for programs like his school and Special Olympics. She's absolutely loving all of it, and she can't believe she didn't quit sooner. I think if you can find something that's close to your heart like that, it can be really fulfilling. And like Jen said, you could always go back to working if you find that you're bored.
Good luck with your decision!
~Anna
