haha, its babysitting - if you like kids, which i would think you do b/c you work in a preschool, do it! i babysit 3 little girls (8, 4, and 1) on a semi-regular basis - i love it but thats just becuase i love children. its an easy job, and again since i love kids its enjoyable. and, its easy money - i usually babysit for about 3-4 hours at a time, and the mom tesnds to give me about $10 an hour - basically because they love me - but i've never "charged" a certian amount, i like doing the job, so whatever they give me is fine.
if you decide to do it - don't worry about them calling you every week asking you to babysit, you can say no i'm busy