We got Nexus and Global Entry in November 2011, and after they allowed GE for children under 14, I enrolled my kids several months ago.

On our return on FCO-FRA-SEA last week, the customs officers were surprised that all four of us had GE. They had never seen a family with young children who had GE.

It did make a big difference. We would have had a 30 minute wait in immigration and a long wait at customs, as two DL flights from AMS and CDG came in just a few minutes before we did.