This depends on why you are taking lessons. There are so many benefits from swimming with infants that include a healthier immune system, development of curiosity and independence and stimulation of coordination and balance. Where else can an infant get such great exercise? Babies are capable of learning to swim, unassisted by the age of 8 months. Since drowning is the #1 cause of accidental death in children under the age of 3, getting an early start will help in the layers of protection, including fencing your home pool, locking doors that lead to the pool, and learning CPR. If your sole purpose is to teach your child to swim as quickly as possible, then taking lessons 3 times per week at the age of 2 or 3 years old would do it. Every year thereafter becomes more difficult and takes more time because of the fear factor.