Infants
Infants and toddlers up to 2 years can benefit from formal lessons, but you shouldn't expect a whole lot.
In fact, those swim lessons won't keep your child safe in the water. Despite everything many private swim schools claim, infant swim classes give limited results.
Most children of that age have disorganized, almost reflexive swimming skills that have no practical value and relation to actual swimming.
Young children (before 2 years) are not developmentally ready to learn the whole spectrum of water survival skills to perform a self-rescue in cases of unsupervised access to the swimming pool. There's no evidence to support that infants are able to transfer early-learned skills to swimming.
Additionally, swim lessons experience can be very traumatizing at that age and ultimately affect your baby's progress moving forward.
Thus, it's better to gradually expose your children to the swimming pool on your own before they are ready to learn. In the meantime, adult supervision is required near water at all times, even when wearing life jackets.
Toddlers
Toddlers (2-3 years) are ready to acquire vital skills in water safety. Particularly, research indicates that toddlers of 3 years are able to learn basic water safety skills.
Typically, a child learns how to jump in the swimming pool and tread water to the side.
Additionally, at that age, many kids tend to follow good water safety habits more strictly than younger children.
Thus, formal swim lessons for children ages 3 and older can significantly decrease drowning risk. However, it's important to note that it won't be a FAST process. You'll have to get multiple lessons for 8 to 12 weeks before your children eventually learn key skills.
Older Children Learn to Swim Faster
While it's true that some children can learn skills in swimming at a young age, most kids learn how to swim after they hit 3 years mark effectively.
So, if your kid has only mastered blowing bubbles, trust me --
It's OKAY at a young age.
In fact, most studies indicate that practical lifelong skills such as entering the water, swimming, turning, and getting back to the exit were fully achieved after regular swimming lessons in 4,5-year-old kids. Additionally, AAP confirms that young children are not "developmentally ready" to effectively learn in swim lessons until they are 4.
So, all the worried parents out there, if your kid is 4 years or older, you just reached a perfect swim time! Just because they didn't start to swim early doesn't mean it's a hopeless case. It's more than usual for other kids, too.
I wrote a complete manual on choosing the RIGHT instructor; you can check it out here. Here's a brief overview what every parent should consider before choosing one swim school over another: