My friend passed away three years ago and has a boy and a girl. I take care of them both and the boy now is 21 years old. I treat both like my children. So my question is can I hug the boy or put my hand on his shoulders or back to motivate him, and can he kiss my hand like my kids do each day after fajr prayer?

Honorable sister,
This son of your deceased friend is considered a non-mahram (a person allowable to marry). Therefore, you must limit your treatment and physical contact with him to avoid doubtful matters. It is only permissible for you to shake hands with him if there is no fear of temptation (fitnah). You should not exceed these limits, otherwise it may lead to fitnah.