No. The best exersise class is playing and having fun with your baby. Yet they are a nice respite and a good opportunity to get out and meet new moms.
No. They're fun, and they'll give you and your baby a nice opportunity to meet people and get out a bit. But no, I don't think there's any evidence that these kinds of classes actually help with development.
No. Normal, healthy babies develop just fine without exercise classes. Because babies love to move around and play, every day of their lives is a spontaneous "exercise class". Parents should take time out every day to play with their children. If an infant has a developmental delay or some physical handicap, then a structured exercise plan can help improve the desired skills.