I agree with letting your older ones choose. I have a three year old boy and we visit his Dad every Sunday at rehab. No, it's not jail, but honestly my son doesn't know the difference. He sometimes plays with other children there visiting their dads. He enjoys himself and likes to see his Dad. Plus it is a good thing for my AH to see his son.
Your older kids are old enough to understand right from wrong and also the lesson of taking responsibility for your actions. I don't think that seeing you there,especially because it's NOT behind bars, will scar them. You can talk about, and I'm sure have talked about already, why you must do this and that can be a positive thing in your lives. Gwen, you have taken back your life. It's been hard but you've made the best decisions for yourself/your kids along the way. You need to hold onto that.
You are setting a good example to your kids by following thru, not using, and being a responsible adult. I can't see them turning out anything but as really good kids.
Hugs!