Sometimes I feel like I'm going off the looney edge and I only have ONE!

Childcare (or shared babysitting) is a great suggestion. Here are some others:
- join a Homeschool Group
- if you can afford it, let your 6 yo use www.aleks.com for math (mine loves it)
- BBC has a lot of kids games (questionaut, dance mat typing, spanish) that are free, http://www.bbc.co.uk/schools/ks2bitesize/
- check out Hoagies Gifted website
- maybe have the older two play a game (Chutes and Ladders or something) while you work with the little one
- use your local library as much as you can

Hang in there, you'll make it. And, you're not crazy. Your children are gifted. It's hard to tell how much at this age. Hope that helps.