New study shows that young children understand how the sounds they make influence someone else.

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Children as young as 2 years old understand that making loud noises wakes a baby, according to a new study by researchers at the University of Washington.

That may not sound like a big deal, but appreciating how sound volume affects someone else is not a trivial social skill.

Some adults are still working on it.

Just think about all the times you’ve overheard someone’s half of a cell phone conversation while standing in the checkout line or movie theater and wondered how they could be so oblivious to the people around them.

“Perspective-taking is a lifelong skill that’s super important,” said Andrew Meltzoff, one of the study’s co-authors, who co-directs the UW Institute for Learning & Brain Sciences.

Previous research on how that skill develops in small children has focused on visual perspective-taking ­– for example, how babies follow a mother’s gaze to see what she’s looking at.

In their latest study, lead author Rebecca Williamson at Georgia State University and co-authors Rechele Brooks and Meltzoff at UW believe they are among the first to explore how that skill develops for inferring what others can hear — which is more complicated feat because we can’t follow someone’s ears like we follow their eyes.

It’s also a step toward more abstract perspective-taking – such as appreciating that someone else might prefer a different ice cream flavor or subscribe to a different political philosophy, Meltzoff  said.

The “don’t wake the baby” experiment involved 48 children, ages 2 and 3.

The researchers created two noisy toys and two quiet toys using see-through plastic tubes that were filled with  bells, beads, feathers or glitter.

Then the researcher left the room and brought back a doll in a bassinett, saying in a hushed tone that the baby was sleeping. Some kids were told that it was now time to wake the baby and some were told that they should let the baby sleep some more, but none were told to be quiet or make noise.

Children told it was time to wake the baby made louder sounds (either by choosing a noisy toy or banging the quiet toy against the table). Children told to let the baby sleep made softer sounds, (either by playing with the quieter toy or by not shaking the noisy toy as much).

Toddlers with siblings were more likely to adjust the noise level appropriately, suggesting that they may know what it feels like to be awakened by a noisy brother or sister.

The study, published in Journal of Cognition and Development, is available here.