My 16 mth old goes to FDC, and although they little ones tend to "do their own thing" they learn sooo much by watching the older ones. And they do play in thier own cute way, they sort of follow each other around like little ducks, and they tend to do things together eg one in the sandpit, and they all go in, even if they do their own thing whilst in there.
My primary reason for FDC was the social aspect at first, as I didnt go to mothers or playgroup. best thing i could have done, I think.
My 2.5 yr old nephew has almost never been exposed to other kids (a 6 yr old cousin maybe once a month and my DS about once a month, and very recently kindermusic) and he is completely socially retarded. His grandma is his best friend and he cries when she takes him to the park if there are other kids there. He has no concept of sharing, and wont even make eye contact with other kids.
Anyway, thats a whole other thread LOL.
What about one of those indoor play centres, or even the ones at the shopping centres?
The more exposure the better IMO.
Good luck.