I think there's one significant difference between a 20 and 25 month old child, aside from the obvious maturity differences. Like I posted earlier, when we called airlines (Delta and Continental) checking prices for our 2 trips next spring, we said we'd be purchasing a seat for our infant too. We were then told by both airlines we called that if the child is under 2 and we purchase a seat for it then it must be in an approved child restraint, it cannot just sit in the seat. For us it's not an issue since our baby will be 2-3 months old and obviously can't sit on its own anyway. We later also checked with 2 other airlines (USAirways and Southwest) since my cousins from another state are joining us on the May trip and will have a 6 month old and both of those airlines said the same thing, that we must have a seat for the child since she's under 2. So for your 25 month old, it would be 'legal' according to what the airlines told us, but for a 20 month old it would not be, regardless of what is safer. Of course, the flight attendants really can't tell if your child is 23 or 24 months so odds are they won't even mention it, especially if you end up holding the child anyway. Of course, our child won't be here for another 5 months, and I may feel differently when he/she arrives, but right now the way I look at it is that if we travel in a car I'd use a car seat so why should it be any different on a plane?
