Haven't done the DC flight but have done many flights into US with little ones. Just bring the car seat. You will get some "why is she even bothering" stares and they will probably ask you if it is FAA approved like your smuggling heroin in it but go with confidence if it says FAA approved. You will mostly definitely have to go through customs and re-check bags. Always have to do this in the initial city you land in the US. If you are GATE checking a stroller with QA make it very, very clear you want it at the GATE. They suck at this and ALWAYS send it to luggage. Good luck with the flight!
Haven't done the DC flight but have done many flights into US with little ones. Just bring the car seat. You will get some "why is she even bothering" stares and they will probably ask you if it is FAA approved like your smuggling heroin in it but go with confidence if it says FAA approved. You will mostly definitely have to go through customs and re-check bags. Always have to do this in the initial city you land in the US. If you are GATE checking a stroller with QA make it very, very clear you want it at the GATE. They suck at this and ALWAYS send it to luggage. Good luck with the flight!