LO came home from school yesterday and said some girl from another class yelled at her on the playground and said she (my LO) couldn't play with them (this girl and her friends). Being her mom I got sad because these kids are only 3 and 4 years old.

When do you think bullying starts? Best way to explain this type of thing to a young LO? Trying to figure out if this is just 4 year old behavior or actual start to bullying.