When we brought Baby S home from the hospital six months ago, his big sister, B, was instantly smitten. She leaned her curly head over his car seat, tickled his toes and cooed like a pro — in a voice squeakier than Mickey Mouse’s.

B’s voice — already a happy toddler squeal — sounded as if she'd sucked in some helium. My husband and I wondered about her higher pitch. Are humans hardwired to chitchat squeakily to babies, or did B pick up vocal cues from us? (I don’t sound like that, do I?)

If I’m like other mothers, I probably do. American English-speaking moms dial up their pitch drastically when talking to their children. But dads’ voices tend to stay steady, researchers reported May 19 in Pittsburgh at the 169th Meeting of the Acoustical Society of America.

“Dads talk to kids like they talk to adults,” says study coauthor Mark VanDam, a speech scientist at Washington State University. But that doesn’t mean fathers are doing anything wrong, he says. Rather, they may be doing something right: offering their kids a kind of conversational bridge to the outside world.

Scientists have studied infant- or child-directed speech (often called “motherese” or “parentese”) for decades. In American English, this type of babytalk typically uses high pitch, short utterances, repetition, loud volume and slowed-down speech. Mothers who speak German Japanese, French, and other languages also tweak their pitch and pace when talking to children. But no one had really studied dads, VanDam says.

So he and colleagues outfitted 11 preschoolers around 30 months old with recorders placed in tiny shirt pockets and taped a day’s worth of sounds and speech directed at the kids — more than 150 total hours of audio. Then the team fed the data into automatic speech recognition software that analyzed the pitch of each speaker’s voice.

Every mom in the study upped her pitch when talking to her child — by about 40 hertz. (The pitch of a typical man’s voice is around 120 Hz; a woman’s is around 220 Hz.) Such a jump is definitely noticeable, VanDam says.

Unlike moms, whose average pitch soared and bounced up and down as they cooed to their kids, dads were much less likely to talk in a squeaky voice, VanDam’s team found. “I wouldn’t say that dads never do it or that dads can’t do it,” he says. “They just do it much less frequently.”

Infants pay more attention to the high-pitch speech of their moms than the low notes of normal adult conversation, earlier research has shown. This extra attention could boost kids’ language skills. A 2014 study in Developmental Science found that babies who interacted one-on-one with a babytalking caregiver babble more and say more words as two-year-olds compared with infants who miss out on the special chatter.

Kids could also develop their language skills by practicing different styles of speech with different parents. Using an informal style with mom and a more formal one with dad “might give kids a rounded ability to engage in different kinds of speech,” VanDam says.

His study focused on traditional families, with mom, dad, and child all living together under one roof. He doesn’t know how nontraditional arrangements, or other factors — whether or not mom or dad (or both) work outside the home, for instance — might influence parents’ speaking styles.

And VanDam can’t say whether or not my 4-year-old daughter picked up her sweet, Alvin-and-the-Chipmunks voice from me. But she may be following in my footsteps and those of other English-speaking American women. Because we, apparently, are a squeaky bunch.

Meghan Rosen is a staff writer at Science News. Follow her on Twitter: @MeghanDRosen