I know I've already posted, but I keep following this thread because it interests me. As the thread continues there are some things that keep popping up that I feel a need to comment on.
The first is that if one child says yes and the other doesn't jump up for it. By talking to the kids together, one may feel pressured to do something with their money they may not want to. If the OP says, "Hey, wouldn't this be great, but..." there may be (unintentional) pressure placed. If the kids are talked to separately and then left to discuss it together later, one might put the pressure on the other.
Second, we always view vacations as an extra. It is not the same thing as contributing, imo, to keeping a household. Being required to pick up around the house and going to WDW just aren't on the same page. It is not about learning responsibility. Contributing to a water bill that was left running is about learning responsibility. And, hopefully, there was a lesson about how bad that is for the environment too.
Third, they were just there is September and are going back in May. This isn't a "special" trip. It's an extra trip. Not a bad thing, but they may not be appreciating it as much as they might otherwise. This trip isn't even their idea (unlike the pp child with the wii). They haven't been begging to go again. It is not the same as saving up for it (like the pp with the vacation fund piggy bank). It is an impromptu trip arisen from a last minute opportunity. They have barely had their money when they are being asked to spend it on something else; there has been no sacrifice. I don't think they will get much in the long term to contributing to it. If anything, I'm afraid it might teach them any unexpected windfall should be spent immediately without thinking of the long term.
Next, there are different in components to a trip. Contributing to the basics of a trip (food, lodging, transportation) is not the same thing as buying the extras of a trip that is for their own personal use (souvenirs). The former is the parents decision, the latter the child’s. Children should pay for their decisions, not the parents. Unless the kids are deciding on dates, transportation mode, researching the tickets, etc, they don't really have the say.
If it were me, I'd say we just can't afford the trip. I understand the OP is saying
extra cash for the trip only (no debt, nothing else neglected), but if it were my family it would have to be
my extra cash, not my kids, to equal a trip.
The way I see it, it isn't the same thing as teaching your child each and every time they get money that 20% goes to savings account that can not be touched, 10% goes to charitable acts and then the rest can be spent they way they want. This is the recommended model by experts to teach kids how to handle money and promote long term financial responsibility, btw. Actually, following that mode the kids should have $45 in savings, $22.5 to charity and only $157.50 to spend as they like--barely enough for the tickets; only $7.50 left for souvenirs when they get there, which we all know does not go far. Are you (general you, not just the OP) really going to tell the kids they get to pay to go, but have no options to do anything extra when they get there that they might want and would have spent their money on? Would that be a fun trip?
I don't think the OP is a horrible parent--or wrong in any way.
I just wouldn't do it and I haven't been swayed by any of the pro-contribution arguments here. I find too many fallacies with them.