K.P.
My only experience with the Y is in Arlington. My nephew and niece played 3 and 4 year old, last year. It was fun for their age, most of the kids didn't know a lot, but seem to have fun. It's great to get them moving. Ofcourse you did have a few that played with the grass and didn't pay attention, however, on the other spectrum their were a few that you could see were good at the game and might play it for years to come. I say go for it. It's the most inexpensive way to get them started.