This helps you to find out who they live with, family dynamics, etc. and also perhaps about other cultures.
Ask your mentee(s) to draw their immediate family tree (some may have lots of relatives so it may be best to restrict it in some way), which can include best friends and pets. They could do this either as a proper diagram or draw an actual tree and write names on the branches.
Ask them to bring in photos of their family and in conjunction with their drawings talk through who they are.
Please note that some students may feel uncomfortable with this exercise if they consider their family to be different from the norm. Try to find out a bit about their backgrounds before using the activity with a group.