A couple of months after dd's second birthday, we started the church parents morning out program...2 days a week, 2.5 hours each time.
She did cry a bit at first, and the teacher was wonderful with holding her, comforting her, etc, which I think is very, very important. (Of course, lol.) Ok, so that lasted about 3 days, and she was totally in love with the place. It was hard for me not to be a little hurt actually, as she ran to Miss Sarah and left me in her dust, lol.
Emmaline has also really, really bloomed from the consistent social interaction and loose routine. (Music class every Friday, stretches each morning in the circle, etc...but most of the day is fairly unstructured.)
Visit a few places, or have dh do it, and see what you like. Any place worth it's salt will let you pop in unannounced, at least to walk around for a minute.