It totally depends on the airlines. Many airlines have stopped preboarding families. I have occasionally been able to preboard when traveling with carseats to install, but even then, it has been at the mercy of the gate agents.
TBH, I prefer not to preboard with the kids. It just gives them more time to have to sit around on the plane. When we have a carseat or two to install, I usually like to preboard with the seats to give me time to get them installed, then DH waits until the last possible moment to bring the kids on board.