I've been taking mine to playgroup for a couple of months now. It's a multiples group too which is great cos there are other twins and even a set of triplets there as well as singleton children.
It gets really noisy and manic and it's a pain to get to (it starts at 9am on Monday morning

). I get there for 10ish for an hour and a cuppa. The children really enjoy watching all the older kids running around and I think it helps them get used to being around other children too. One of the best things is they are totally knackered afterwards and have a lovely long sleep!
There are a couple of other mums that I've got friendly with that have twins slightly younger than mine and we meet up outside of the group too. It's nice to have a natter with other folks who understand what you're dealing with.
Highly recommend it Wobbles. Just gotta find the right group.