What kind of job would you get? What is the salary range you'd be shooting for??
I mean, I guess if you were going to be working minimum wage and will have to spend extra just to work (gas, work clothes or uniform, lunches out, after school care, etc.) then the tax rate might make it hard for you to end up really making any money at all. If you are hoping for a pretty well-paying job though, I think the overall effect would be an increase in your family's income which would make it easier for you to meet any financial goals you may have. You can google for a 'second income calculator' to start estimating how much you'd be able to really contribute.
Why are you considering working? Unfortunately DH & I don't have the luxury of choosing whether or not to work so it's admittedly a bit hard to relate to your issue. But there is no rule that you have to work just because your kids are in school full-time.
PT vs FT is what is really would come down to. Option 1 would be pt while dc are in school, which would most likely me a close to min wage job w/NO benefits. Option 2 look for a career like job, with FT year round hours and benefits. Option 1 financially would not be worth it with all the costs associated with just and at the 25% tax rate. Option 2 would be financially OK at 25% especially with the benefits however, both dh and I do not want that kind of family lifestyle. Now, if I could find a well paying pt job, that would work.