1. to contact someone in order to report or find out information
check in with parents/spouses/children
To 'check in' with someone usually means to get in touch with them or make contact with them in order to establish how things are. You might 'check in with' someone to let them know you are ok, to see how they are or to relay important information. If you are working on something you might 'check in' with your boss to see if you are on the right track. This is a popular phrasal verb used in social and professional situations.