One suggestion for those traveling with rear-facing seats...
If both parents are traveling, one parent can sit in front of the child, and the other parent can sit beside the child. That way, the seat that will not be reclining contains a member of the child's party, and you don't have to worry about complaints.
We have done this a few times.
When that wasn't possible, we have offered the passenger in front of the child's seat a Starbuck's gift card. We approach them immediately upon boarding, so that we are reaching out with a peacemaking gesture before they even have a chance to complain. Everyone we have encountered has been gracious, and most turn down the offer of a gift card.