I know one of three things will happen:
1) they will spend over their limit but find something they love love love such I either bankroll the difference or seem like a world class miserly curmudgeon or...
2) Binge shopping until the card drops.
The problem with binge shopping of this nature, is the desire to spend outweighs the actual need to acquire, but the young shoppers won't rest until the amount left on those pieces of plastic is less than a nickel. So what if we have to purchase a pack of gum they don't chew, it's worth it to have that credit card balance read .03.
Offering my own two cents, like maybe for saving the money or spending some, not all, is met with a stare that translates to "Mom, are you nuts? We did the dishes for you, of course we're going to spend it all."
And so it comes to pass, we own a Pickachu dressed in a Pirate costume, some silly putty, pens each color of the rainbow, three t-shirts with Halloween themed designs, an umbrella festooned with ice cream cones and some Shopkins, (which are plastic foods with cute faces). The balance reads 1.39 and my daughter runs to get a tube of mini-M&M's.
Walking out the door, carrying her bounty, my daughter remembers, "I lost my water bottle at the party." "I remember." I said.
"Can we go back into the store so you can buy me a new one?" she asks. "I'd buy it myself but I'm all out of money."
And that's #3 of what happens.