We have DD 7, DS 10, DD 11, DD 13.
The kids have been saving for WDW for some time.
We took a spontaneous trip to DLR in August. We told them to keep their money for WDW and we would pay for their goodies at DLR. We gave them each $30 on the first day and told them to spend it as they pleased for the 3 days we'd be there. We didn't want to be bothered with all of the yes/no decisions.
Oops.
DD 13 and DS 10 blew the whole thing the first day. After a strained 2nd day we gave an additional $20 on day 3.
For WDW, we gave the kids $20 from their savings (each) on the first day plus a $10 gift from us. Most of them had $100-150 saved up. We said that for the remaining amount of their savings, they could buy things with our approval. On each subsequent day of the trip, we gave them each a $20 gift from us. Any cash in their pocket, whether from their initial $20 withdrawal from their savings or our gifts were there's to spend as they wished without asking. But in order to tap the balance of their savings, they had to come to us.
They played it pretty well. And on the last day, when we were at the animation gallery store at Disney-MGM, 3 of them had enough money for art sets, sketchbooks, and character drawing books.
That was pretty cool.
We paid for all group food and snacks. If the family stopped for popcorn, we paid. If a kid elected to get popcorn while the family was headed off to something else, they paid. We paid for ride photos that we liked. We bought a round of T-shirts at various times at our discretion. But they bought shirts that they liked as well.
It worked great. So for 7 days, each kid, in total, had complete control of $150 and access to about another $100 with our approval. In that way, each kid came home with something we thought was worthwhile and at the same time, they enjoyed buying things that only they could understand the value of.
And it may seem inverted that we exerted parental control over their savings while the kids had free reign on the money we gave them each day as a "gift", but in the end, the money that we guided them on from their savings actually went towards the durable items that they brought home. So when they look at those things (ie. the art supplies/sketchbooks/drawing books), they talk about how that came from their savings.