I highly recommend teaching your kids swimming yourself. With the first, we did one short set of swimming lessons at the age of 3 or so. It was cold and unpleasant and regimented, and he didn't learn to swim anyway.

After that we just went to a nearby pool regularly in the summer, and allowed him to have fun in the water, just playing around naturally. And then you give a little hint occasionally about strokes, and boom, they're swimming.