I don't see how that could even be an issue. I'm not sure what kind of carseats you're thinking of, but the carseats we have are latched in and they don't get unlatched unless there is a reason to remove the carseat...which is only in the unlikely event that someone else needs to sit in that seat, or when the child gets old enough that he no longer needs the seat.
In other words, you don't latch and unlatch the carseat. Once it's latched, it's latched and there is no reason to come out to the car and find it unlatched. It's not matter of remembering whether or not you latched it, because you never unlatched it in the first place since you put it in. At least that's our experience.
When we went to Six Flags a couple years ago and we needed the seat for an adult (our son stayed with his Grandma that day), since we were all going in my van, then we took the carseat out. I think that's the only time that the carseat has needed to be unlatched, and our son is over 2 years old now.