Playdates are easiest when our friends also have two kids with a similar age gap! But playdates are also fine when our friends have one kid, about the same age as our eldest. (Our youngest daughter is used to playing with her brother's older friends.)

We don't have many friends with 3 or more kids, but I'm guessing it wouldn't be a problem as long as the age gap wasn't too big!

Do your parenting friends tend to have the same number of kids as you?