• The accomplished swimmer is teaching his two youngsters how to swim — he said his eldest, 2-year-old Boomer, has "got a nice little stroke going," and can swim butterfly and freestyle. 
  • For Phelps, the most critical primary swimming lesson for kids is to make sure they are comfortable in the water, especially when they first submerge their heads.
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When Olympian Michael Phelps was a little boy, he only swam on his back. 
Phelps, the 33-year-old retired Team USA swimmer, has more Olympic medals to his name than anyone on the planet. But he said that as a tot, he didn't love to splash around.
"I was a kid who started on my back because I didn't like to get my face wet," Phelps told Business Insider. 
With his own two young boys, Boomer and Beckett, Phelps said he wants things to be different. So he started getting them into the pool when they were just 3 to 4 months old. 
"The biggest challenge is really just trying to make sure that they're as comfortable as possible in the water," he said. "And every kid is going to learn that in a different way." 
Pool safety is crucial
 Pools can be dangerous places for tots: Drowning is the leading cause of injury-related death in children from 1 to 4 years old. 
"Many of these deaths occur when children are not expected to be swimming or when they have unanticipated access to water," ER doctor Sarah Denny, who co-authored a new report on preventing drowning, said in a release.  "Toddlers are naturally curious; that's why we must implement other strategies, such as pool fencing and door locks."
Phelps said his pool is fenced off, and his kids know to stay away from the drains and never swim without a parent alongside. There's no evidence that teaching kids to swim before they're 1 year old, as Phelps did, has any impact on a child's drowning risk.
But if your kids can enjoy being in the water before their first birthday, water play classes might "help your infant get used to being in the pool," the American Academy of Pediatrics says.
That's exactly what Phelps was hoping for with his boys, who are now 1 and 2.
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Boomer Phelps and Michael Phelps at a swim class.Dia Dipasupil/Getty Images for Huggies
Kids should learn to tolerate a wet face 
"I think the initial shock of going under water, that's probably the scariest point," Phelps said. "Just trying to stay comfortable when your face does submerge." 
To prepare his kids for the shock of a wet face, Phelps said he started blowing air into the babies' faces early (which instinctively helps infants hold their breath, a phenomenon called the 'bradycardic response'). He also would often "dunk them" into the water to get them used to that feeling he used to hate. 
The strategy has paid off. 
"They both love jumping off the edge," he said. "They have zero fear in the water."
Phelps said he and his wife Nicole are still getting their youngest, Beckett, used to enjoying the water in new ways.
"Beckett just kind of splashes around, plays with toys, and he'll sit in a little float that we have and kind of just splash around," Phelps said. 
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Phelps competes in the Men's 200m Butterfly Final at the Beijing 2008 Olympic Games in China. Phelps finished the race in a time of 1.52.49, a new World Record.Paul Gilham/Getty Images
There's no rule about the right age for swim lessons 
Pediatricians emphasize that you don't have to teach your child to swim as early as Phelps has. Every child is a little different, and there's no use in pushing a baby into the waves.
But by age four, the American Academy of Pediatrics (AAP) says "most children are ready for swim lessons," including basic water safety skills like learning how to float, tread water, and get in an out of a pool on their own. If your child hasn't started learning swimming basics by age 5 or 6, the AAP notes, "now is the time!"  
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Nicole Phelps, Michael Phelps and Boomer Phelps in the pool.Dia Dipasupil/Getty Images for Huggies
Phelps, who boasts an impressive 6-foot-7-inch butterfly wingspan in the water, said he already sees a budding swimmer in his older son, Boomer, who will turn 3 in May. Phelps said "he's got everything down" and swims freestyle and butterfly.
"He's got a nice little stroke going," Phelps said.
Those are the words of an adoring parent, of course, but the analysis also comes from the world-record holder in the 100-meter and 200-meter butterfly events. The Phelps family recently announced that a third swimmer baby is on the way later this year.
"Three kids under four will be ... that'll be a handful," Phelps said.
Yet again, he plans to get his new baby's face wet in the pool just months after he or she emerges from the womb.