I’ve gotten it in two flavors.
One is people who are so convinced that life has no meaning without children they feel like they are saving you by pressuring you to have kids.
The other, and far more angry, seem to have had kids because they thought they had too, or had a “happy accident”, and aren’t actually happy about. They see you as the life they could have had.
First time I ever used one was 2004 following the grateful dead on an east coast tour.
One nice benifit was we’d come into town from the opposite direction of the caravan, avoiding a ton of traffic and finding the back route to the venue. Almost always got us better parking and way shorter lines into the lot.