I have found that it's best to find other multiples to playdate with. That way they better understand the dynamic. I have seen singleton be somewhat everwhelmed when they start to play with one of my kids and end up playing with all 3.
It's like one makes a friend (at a playground or wherever) and the others just assume they can be friends with the person too. Sometimes I even see them trolling for new friends rather than playing with each other.

I haven't had too many playdates either because I'm not sure what to do with the kids who don't have a friend come over. Hopefully those with older kids will be able to share some good advice soon.

Andi
g/b/g
6 yo triplets in kindy