How young is too young to use a smartphone? In a growing number of families across the country, infants and toddlers are deftly swiping and tapping away even as they wobble toward their first steps.

The swift adoption of tablets and smartphones has sparked an unprecedented explosion of software games, videos and educational programs aimed at the very youngest minds, dramatically increasing the amount of time these children are spending in front of electronic media. Experts estimate that tens of thousands of kid apps are offered on Apple and Google Android devices, with titles such as BabyPlayFace and Elmo’s Birthday.

That worries some educators and child-development experts who view the flood of baby and toddler apps with trepidation. They warn that children already spend too much time in front of TVs, DVD players and computers.

For children 2 or younger, all those screens can have a negative effect on development, according to a recent statement by the American Academy of Pediatrics. If you really want to help boost brain power, the best solutions can be found with unstructured play, the academy said.

“Kids need laps, not apps,” said Frederick Zimmerman, an expert on media and child health and the chairman of the Department of Health Service at UCLA.

Some harried parents say they rely on the devices to prevent their child from melting down in a restaurant or an airplane or a long line at the grocery. One in five parents uses a smartphone or tablet to keep children distracted while running errands, according to Common Sense Media, a child safety advocacy group.

For Paula Mansour of Falls Church, allowing her 2-year-old, Maggie, to play a few rounds of Angry Birds as she prepares dinner helps her keep the household running smoothly and stress-free.

She monitors Maggie’s smartphone time — and that of her 6-year-old sister, Kayla — and does not see the harm in short sessions on her Samsung Galaxy a few times a day.

Aside from Angry Birds, Maggie plays with Kids Doodle and ABC Views — apps that promise to help children get an early start with preschool skills. “She’s learning and having fun,” Mansour said. “I don’t see any harm in that.”

Kid-app explosion

Just about every category of learning is covered in Apple’s and Google’s app stores. Get your toddlers to trace letters with their fingers on one of dozens of apps aimed at budding writers. Baby Sign Language teaches infants the signs for cow, foods and other objects. Math Ninja offers drills on multiplication and division.

Want to read “Humpty Dumpty” to your newborn? The Nursery Rhyme app will do that for you. BabyPlayFace has been featured in Apple’s iTunes store, with 250,000 downloads. It teaches infants first words in different languages through animated baby faces.

Apple and Google tout their mobile devices as revolutionary tools for learning and fun — and helpful distractions for the modern parent. They promote Angry Birds and Cut the Rope as children’s games that consistently rank among the most popular apps.

“Every parent could use a hand. Keep up with your kids or just keep them busy with family-friendly iPhone apps,” Apple pitches to users on its iTunes store. Apple rates apps with a minimum age of 4. Apps on Google’s Android system do not have an age minimum.

There has been no definitive study that shows whether apps on mobile devices are harmful for youths. And although lawmakers and regulators have been seeking to strengthen federal rules that protect the privacy of children online, few have examined the rapid growth of mobile content getting in front of very young eyes.

Some educators are dubious of the educational promises espoused by app developers.

Zimmerman co-authored a report in 2007 that debunked marketing by Disney’s “Baby Einstein” DVD series touting early developmental benefits. He said it is too early to say that apps are any more effective at getting children ahead. The American Academy of Pediatrics agreed and warned against developers that advertise their products as “educational.”

More than a quarter of all U.S. parents have downloaded an app specifically geared for their child, according to a survey released this month by Common Sense Media. Children 8 and younger spend about 21 / 2 hours a day in front of a TV, computer or mobile device and about 30 minutes with books, according to the survey. That’s almost one hour more than the daily screen time for young children in 2005, the group said.

Interactive learning

Not every child-development expert is skeptical of mobile devices. Some note that smartphones and tablets offer children a far more interactive experience than parking them in front of the television. “The wrong way to think about this is not whether to turn it off or turn it on but about taking responsibility for what content gets in front of our children,” said Liz Perle, co-founder of Common Sense Media.

Sherri Richardson Burgan of Portage, Pa., is convinced that her iPad is making her toddler smarter. Two-year-old Colton won’t sit still to draw with crayons and wriggles out of his mother’s lap during story time. But on the tablet, Colton enthusiastically points to shapes, letters and colors and identifies them by name.

“A circle! I did it!” he cheers.

So, like scores of parents, Burgan has been on a frenzy downloading games, educational programs and videos for her youngest. Colton is usually on Burgan’s lap or at least nearby when he is on the iPad, so she does not put any limits on his time using the tablet.

The apps will “let him reach his full potential,” said Burgan, a stay-at-home parent with three older sons. “He got it right away. He knows how to turn on the iPad, find his favorite apps and get started.”

Kid apps are among the fastest growing in Apple’s store. BabyPlayFace founder Jacob Slevin said Apple sent a team to New York to meet him last week to help improve the app, which he hopes to expand into various baby body parts. Parents have sent him video testimonials from around the world, saying how much they love the app.

Slevin does not have children. He is not an educator. But he did help his younger sister with speech therapy exercises, and he is a tech enthusiast who sees no limit to the potential of apps.

“My pediatrician is now a consultant for us and is replacing all the silly toys in his waiting room with iPads,” he said.

But before one tosses out toys for tablets, parents should remember that nothing beats real-life learning, said Howard Gardner, a professor of cognition and education at the Harvard Graduate School of Education.

And parents are modeling their own smartphone addictions to a whole generation of children growing up with apps, he said.

Gardner’s advice for those parents who want to get their kids ahead: walks in the woods, visits to museums and building with tinker toys. “You can’t replace the human imagination,” he said. “There’s no app for that.”