I have two kids. Ages 5 & 4. This makes me a parenting expert. One thing I can say (because I did it) is that if you don't have the money or don't want to shell out the money - skip the swimming lessons for the little ones. You might feel pressured to do it or feel that Little Johnny NEEDS to take swimming lessons at age 3 so he doesn't drown. Honestly, I feel like my kids have gotten much more out of me just taking them swimming and getting them comfortable in the pool.
Sure, the lessons are a nice little boost to their morals or some crap like that when they pass a level. But quite honestly, they're only usually 30 minutes and they are in a group of 5 or 6 and spend most of the time hanging out on the wall. If you want Little Johnny to get comfortable in the water, just slap on a suit yourself and take him for an hour at least 1 time a week. Once they have the understanding of water and whatnot, sure - go ahead - swim lesson them up so they can learn different strokes and whatnot. Probably around age 6. You're not a horrible parent if you don't put them in swimming lessons at an early age and quite frankly, you might just feel like it's a waste of money.
This post is partially inspired by the group challenge Precious started at Frugal Makes Cents.