After talking with all of you, we decided that we would check the older kids' car seats and have the baby sit in his on the plane. Exactly what did you put the car seats that you were checking in? We are looking at bags on Amazon and are not confident that any of the mentioned bags will fit my DD's RECARO Performance SPORT Combination Harness to Booster. The other two seats are the regular convertible seats and should fit in the standard bags but we have not checked dimensions yet. Do we just put the baby in the Recaro and check the other two? I think that he is just at the lower limits but I'm not confident that he will be comfortable in it.