Between 6 months and 8 months.
Once a child is crawling, usually between 6 months and 8 months, he can learn to swim between two people for fun and roll to a safe, balanced, secure float for safety. Once a child begins to crawl, they are at risk of finding an unguarded body of water and falling in. If they have learned how to behave in the water, they will roll to a float and calmly await rescue.
Between 12 months and 18 months.
Once a child is walking, usually between 12 months and 18 months, the swimmer can learn to swim float swim. A toddler can swim in the proper head down posture, with feet kicking at the surface, roll to a balanced float to rest and breathe, then flip back over to swim to safety. With practice, they can swim longer distances using the swim float swim sequence.
After age two and three.
Once a child is two or three years old, depending how early they began their aquatic education, she can begin Stroke Progression. Small children can easily learn to backstroke from the balanced backfloat. Side breathing is simple as they already have the core strength for a roll. Butterfly and breaststroke are fun to learn when children are confident and secure in their swimming and floating.
Check out this baby swim: