My children had three kinds of playdates. One was where the moms took turns dropping off the children to play. Another was an organized playdate where one day a week the moms dropped off the children for a couple hours of organized play- each mom contributed a special interest or skill when it was her turn, and the most fun for the moms was the coffee/play date where the moms brought their children, and while the children played, the moms sat and had coffee and coffee cake and enjoyed chatting with one another. Be sure that you get to know the moms first- I wouldn't just invite any woman into the house, perhaps a neighbor that you've spoken to for a while and other friends, or someone you met on the playground and seen how she is around her children, etc.
at 9:04 AM on Sep. 16, 2009