When your baby is 6 months old, you can register for a swimming lesson for parents and children. You'll be in the water with your baby during these classes, which are actually a social activity. Your child will not be developed enough to receive formal swimming lessons until 3 or 4 years. Meanwhile, be very cautious when you are near or in the water with your little one.
Many swimming clubs offer classes for parents and children. Ask your doctor, other parents or kindergarten you recommend a good program in your area. Try to observe a class before registering. Instructors should conduct a well organized class and show what parents ask you to do (how to hold the child in the water, for example), and there should always be a lifeguard present.
Other things you should provide a center that offers swimming lessons for kids: a pool or heated pool that makes entering the water it less traumatic for your child (and more enjoyable for you), and a relatively small class (not more than ten pairs of parents and children) so you can listen to the teacher and have enough room to play in the pool.