Part-time jobs that fit around childcare - 11 months and counting

I am looking for part-time work that fits around school hours and found a few evening shifts near Omaha. I have read a lot of threads here and could not find my exact situation. Shifts are four to six hours and the pay is weekly. Is the schedule really fixed?

Ask whether the schedule is posted in advance and how they handle swaps. It matters a lot with kids.