A new British study has revealed that babies may not yawn back in response to a yawn because they appear to be exempted from the 'contagious' nature of yawning.
This is in stark contrast to adults, 50 percent of whom will yawn if they see another person yawning, a phenomenon known as contagious yawning.
In the first part of the study, James Anderson and Ailsa Millen from the University of Stirling asked mothers to record when and how often their children yawned.
Babies and toddlers between the ages of 6 and 34 months yawned most after waking in the morning or after naps, but only yawned on average about twice a day.
This is much less than the average seven to nine times per day that an adult yawns.
The mothers did not report any contagious yawning in their children.
In the second part of the study, babies and toddlers with an average age of two years were shown videos of babies - some yawning and others not.
Only three of the 22 children yawned when they saw a baby yawn on the video.
"The largely negative video results confirm that infants and preschoolers are much less susceptible to psychological influences on yawning when compared with older children and adults," ABC Science quoted the authors as saying.
Previous studies have shown that children under five years don't tend to contagiously yawn, but by the time they reach 12 years, they are doing so at the same rate as adults.
According to Anderson, this may be because contagious yawning has been shown in previous studies to be a sign of empathy, and children don't develop this trait until they are between three and six years old.
"Young children may also do less contagious yawning simply because they don't have the same pressures or social inhibitions as adults: They yawn where they like and when they like," he says.
The study appears in the journal Biology Letters.