Researchers suggested bullying begins before children ever set foot inside a classroom.

In the past weight-related bullying has been looked at in older children and teens, but this recent study focused on primarily six-year-olds, HealthDay reported.

"I was very surprised by how young these kids are," Rachel Annuziato, an assistant professor for clinical psychology at Fordham University in New York City, told HealthDay. "I think our understanding of bullying is that it's something that starts a little later cognitively and developmentally, but this suggests that isn't the case. From the day kids walk into school, this is a concern."

Researchers have typically believed bullying behaviors were primarily learned in from other children, but these new findings suggest they are often picked up outside of school. Obesity was found to make boys more likely to bully and be bullied.

"Kids who are being picked on might start to think this is the way to fit in, to pick on other kids," Annuziato said. "That becomes their way to assert themselves after they've experienced bullying."

The findings also believe some insight can be gained into the link between bullying and obesity itself.

"A lot of these risk behaviors may have to do with self-regulation, self-discipline and decision-making, which gets into the executive functioning of the brain," Susan Tortolero, a professor of public health at the University of Texas School of Public Health in Houston told HealthDay.  "It could be that poor coping is going on here, too. They could be expressing aggression because they're being bullied and they don't know how to cope with it or express it."

To make their findings the researchers surveyed 1,300 Dutch children and their teachers. They looked at whether the children were bullies or victims and instances of "physical (hitting, kicking); verbal (teasing, name-calling); relational (being excluded or shunned); or material (personal items hidden or broken)," HealthDay reported. They were classified as having a normal weight or being overweight or obese.

The researchers suggested modeling healthy social behavior in children and focusing on building up their self-confidence.

"If your child has a risk factor for kids picking on them, it's really important to give them skills to cope with those things and to build their self-esteem," Tortolero said. "If you teach your children to problem-solve and how to make decisions, then they will be more successful."