Some of the other comments have some good ideas as to why that is--motivation to earn more, management not wanting to fire parents as readily, etc.--but I wonde

Some of the other comments have some good ideas as to why that is--motivation to earn more, management not wanting to fire parents as readily, etc.--but I wonder if on top of all of that, parents have some other selection effects going on. Maybe whatever hoops must be jumped through to get married and have children are similar in size and shape to hoops that help in the workforce, so group averages move a bit in some positive way. Time for some light reading...