Philly is my "home" airport too and you are right - it is often a madhouse at the USAirways check-in line. Early check-in or kiosk check-in at the airport is so much easier, especially with children in tow. It is worth a try. There is nothing on the site that prohibits checking in on line when infants are involved (none that I saw anyway). I agree it would be a huge help!
And given the recent labor issues with the airline, I don't believe things will improve any time soon. I once waited in line close to 2 hours and barely made my flight. And I've had my seat changed numerous times as well. Those are just some of the reasons I switched over to Southwest and I'm trying to convince the rest of my family to do the same. USAirways, in my opinion, has not been customer-service oriented for some time. I can shake off the odd incident, but it seems to have become the norm in recent months. It is sad that they don't seem to realize that this drives customers away.