Very young children pick up cues on how to behave by watching adults' emotional interactions and by "eavesdropping" on their conversations, a new study shows.

"You might want to be very careful about the emotions you're communicating to other family members if your toddler is around," Dr. Betty Repacholi of the University of Washington in Seattle told Reuters Health.

Babies as young as one year old will change their behavior in response to another person's emotional state, if they are the target of emotional cues such as facial expression or tone of voice, Repacholi and her colleague Andrew N. Meltzoff note in the March-April issue of the journal Child Development.

But it hasn't been clear how infants will respond when an emotional social interaction doesn't directly involve them. To investigate, Repacholi and Meltzoff performed two experiments.

In the first, 96 toddlers who were 18 months old watched a person, "The Experimenter," playing with an object. Each infant went through three trials with a different toy. A second person, "The Emoter," then entered the room and either scolded the Experimenter in angry tones, for example saying, "That's aggravating! That's so annoying," or spoke neutrally to the Experimenter.

The "angry" Emoter either stayed in the room while the child was offered the chance to play with the toy, but kept a neutral facial expression, or left the room beforehand.

When the Emoter was angry and stayed in the room, the infants took an average of 5 seconds to reach for the toy, but when the angry Emoter left the room, or the neutral Emoter remained in the room, the infants grabbed it within 1 second.

In a second series of experiments, with 72 toddlers also 18 months old, the angry Emoter either faced the infant or turned her back to the infant after her outburst. In a third group, the Emoter remained neutral, and faced the infant after she finished speaking with the Experimenter.

While the angry Emoter's back was turned, the researchers found, the infants "eagerly played with the object," but when she was facing them, they were significantly more hesitant to touch and play with the object.

Analysis of the infants' facial expressions found that they were not upset by the angry outbursts, but showed "great interest" as they watched the Emoter and the Experimenter interact.

"The children very clearly understood that someone else was getting into trouble," Repacholi told Reuters Health. "They understood that that information was still very relevant to their own situation."

Previously, she noted, it had been thought that babies only took in and learned from social cues when the cues were directed toward them.

"If you're in the process of perhaps scolding one of your other children, you should be aware that your toddler might be learning from that," she added. "That could actually be a good thing."

But the findings also show that these emotionally savvy youngsters don't know that a behavior is still not OK even if the scolder has left the room or can't see them, Repacholi said. "If the cat's away the mouse will play...that's very sophisticated knowledge as well."