It's fair to exchange favors
Terri has been busy, so her friend has been taking her kids to school for her.
Terri wants her children to get a good education.
Terri decides to take her children and her friend's children on a field trip.
Terri decides to take her kids on a field trip without inviting her friend's children.
Terri's friend enjoys a day off from parenting.
Terri's friend feels unappreciated.