Ok, back up.....how did your stbxh all of the sudden decide to let your s go to the Tuesday activities?
As for the subbing....it's different depending on administration, districts, teachers, etc. Everyone sees it differently. Where I am at, you can specify when you sub and where you sub and it doesn't matter if you turn them down. It's first come first serve and that's that.
Personally, I'm avoiding the subbing because subbing is TOUGH. It takes away all that I love about teaching....getting to know the kids, building a rappor that helps you teach them, getting to make the lessons that I know will work, etc. When you sub you get the worst part of teaching...behavior issues, the "easy lessons" that teachers can do fast since they are sick or whatever, someone else's lessons that usually are sub par, etc. Blah! There ARE perks, and I will sub if I need to and make the best of it, but I can see why someone would hesitate.