As if it wasn't hard enough traveling by air with children, United Airlines won't be offering early boarding to families in coach with small children.

United quietly made the policy shift in late April and joins other airlines including American Airlines and US Airways that have dropped family pre-boarding.

The airline says the move was "to simplify the boarding process and to reduce the overall number of boarding groups," United spokesman Charles Hobart told USA Today.

Previously, families with small children flying coach were allowed on aircraft before general boarding -- a convenience for parents to get their children and their things stowed before the crush of passengers.  But now, as more airlines charge for priority boarding, passengers are more willing to pay to guarantee space in the overhead bins for their luggage --space that could be taken by early boarders.

Of course parents can still pay to board early and avoid the mad dash on the plane. Priority boarding programs begin at $9 and up, so a family of four can now expect to pay $36 or more for the privilege.

The good news is that other airlines, including JetBlue Airways, Virgin America and Delta Air Lines, still offer the early boarding convenience for free.  But for how much longer, it's hard to tell.

United's move comes amid airlines imposing fees for passengers to sit in certain seats --including the window and aisle.