J.F.
If you are willing to drive to Woodbury I would recommend Foss Swim School. Their website is www.fossswimschool.com.
Both my kids have taken lessons there and they start as young as 6 mo. The water is heated to almost bath temp and the swimming pool area is also well heated so the little ones aren't so cold when they get out. I think it is a little more expensive than the YMCA but their class sizes are pretty small.