With American, at least as of May 25 when I spoke with a GA, it depends on the airport you are flying out of. At heavy tourist destinations (or flights TO heavy tourist destinations - such as MCO) where there can be dozens of families on a flight, they do not pre-board. However, they pre-boarded out of LAX last time I was there a couple of weeks ago. So, the moral of that story is YMMV!
Last time I flew UA with the kids in January they did preboard us. Don't know if status came into play or if it is their policy. Can't speak to the other airlines.