The Ohr Hachayim explains in Parshas Nitzavim, why the children were standing in front of Moshe on his final day of life. He says, children have the responsibility top influence their classmates and peers in their own way to stop inappropriate behavior. A child who bullies others, and a parent who defends such disgusting behaviors have the blame for the outcome.
Bullying others falls into the category of V’Haniglos, which EVERY Jew is responsible for.