my son is in senior kindergarden ,5 and half yr old,he donts interact other children easily,he is very energetic and happy in home but it comes when to interact with other child he becomes sad and dont say even hi to other child unless i told,even sometime he cry when other child want to play with him.when i say then only he said by but in sad tone,how to deal with this situation,in school his performance is good,he is so silent in school.please help