Anything that is a traveling necessity for a child is at no charge. But I suggest that you gatecheck the carseat, its less likely to get lost. Its a pain to carry it all the way to the door of the plane but you can ensure that they put it on. Make sure you tag it as well. I definely suggest a stroller. Kiddos can get rambuntious waiting the hour or so at the gate for boarding. You can gatecheck that as well and stroll him to see the planes while you are waiting to board. This will keep you from chasing a inquisitive three-year-old all over the airport. Looks like you have everything else covered. It might be exciting for him to sit in the seat like a big boy hopefully you will have a window seat, he might enjoy the take off and landing. Enjoy your trip and be safe!