Are there any "essential" classes for toddlers?

My wife and I want to start our kids taking swim lessons (at ages 3 and 1). We view this as an essential life skill, and thus not something extraneous.

Of course, there are lots of potential classes for kids ranging from sports to music to dance to art and so on. Are any of them more vital than others? We don’t want to be the Type A parents that fill their kids’ days up with activities, but we do want to shape them in a positive way.

This is obviously subject to opinion, but I would welcome suggestions/thoughts from people with experience in this (parents, educators, kids :-).