Children who were overweight at any point during the study also perceived themselves as having worse interpersonal skills, lower social standing, and worse peer relationships. The heavy children also reported having more "internalizing" behaviors, such as social withdrawal or depression.

The fact that teachers' different perceptions of overweight children extended to those who were technically overweight for the first time in third grade suggests that even children who may have been on the heavy side of "average" early-on experience discrimination, Gable said."

Overweight shouldn't be seen as an "either-or" proposition, according to the researcher, but as a continuum. And both parents and pediatricians should pay attention to a child's weight status even before he or she is officially overweight, Gable added.

How to help kids slim down is far from clear, she acknowledged. And working parents are also faced with major obstacles to helping their kids be more active and eat healthier, she added, which are only getting worse with the economic slump.

Parents simply need to do what they can, Gable said, from offering a child a plain carrot instead of a carrot slathered with ranch dressing, or having kids draw and color instead of watching TV. "In terms of what's the solution -- for families it's baby steps," she said.