We have had one since dd was born. I'm lucky where my friends and I had our kids around the same times, all but 1 is a sahm. We get together 2 afternoons a week for a couple hours, usually at my house where it's the biggest. The kids play games, play make crafts whatever. Us Mom's get to talk to other adults
When the weather is nice we'll meet at the playground or park. There is 8 kids 4 moms. If one of the moms can't make it the kids still come, no big deal, but not 1 mom and all 8 kids, has to be at least 2 mom's. If not it's too stressfull.
Enjoy the playgroup I'd be lost with out ours