My parents took the kids to LHR. Checked them in at the ticket desk then hung around with them outside security until closer to the flight. AA rep then came and got the kids, told my parents they needed to stay in the airport until the flight had taken off (in case late cancellation / deplaning etc) and took the kids to the gate. Pre-boarded. Upon arrival at DFW we had to wait outside customs and the kids were walked through immigration, got their bags, then walked through customs and to us. Worked very well.