Originally Posted by
Efrem
As to whether it will be free: that depends on your free checked baggage allowance. That, in turn, depends on the fare you paid and on your United or partner elite status, if any.
That shouldn't matter. Car seats are independent of checked bag allowance with UA and most other carriers as far as I've experienced. It's just that you can only take one car seat per traveling child. The only potential issue here is that the OP's child isn't traveling with him. I concur with others that it probably wouldn't be a problem as long as the kids are also traveling to the same destination on UA, although you never know what kind of person you'll get to deal with at the counter. Definitely good idea to print out your wife/kids' reservations. Won't hurt to check with UA ahead of time.