I taught swimming for many years and I believe parents can do a good job on their own. That being said, I would get some advice about how to go about teaching swimming. This is especially true if you want to eventually have your children swimming strokes correctly. It is very hard to break bad swimming habits when it comes to good strokes. If you are uncomfortable in the water you would most likely do better with swimming lessons.
I believe Red Cross Lessons (done well) a a great way to learn both strokes and water safety.
I also respectfully and gently disagree with the poster who stated that it does not matter how early a child learns to swim. I've taught from infants to older adults and once a child is a past the 4-6 window it is much harder to get them swimming ime. Also, water safety is a life skill... an important one. Children drown every year. Sometimes if they had known how to swim they would not have.