My 5yo son enjoys playing with a girl (Du) in his class but she is friends with another girl (K) who repeatedly tells my son that he isn't their friend and can't play with them. When K was away from school for a week, Du and my son had a lot of fun playing together in and after school. Since K returned, she doesn't allow Du and my son to play together. My son misses playing with Du and feels sad. How can I handle this situation? It's my first time facing this as a parent...of course my heart hurts for my son, and I also want him to be bolder to develop resilience as these behaviours from others will only increase as he grows older. Any tips and advice will help. TIA