Another travel tip!
Have your kids earn their souvenir money for the trip by doing tasks around the house before you go. If they can help you get ready for the trip even better. Let them clean all the trash out of the family car (if yours looks anything like mine this is worth a few bucks but let's be honest about who makes the mess!), let them help with sorting or folding laundry, have them organize the tuperware cupboard, there are all kinds of ways they can help around the house on top of their regular chores to earn some bucks.
Then if they are little, instead of giving them real money give them Beach Bucks! Use your computer to make up cute fake money. The first time I did this I made Beach Bucks because we were going to the beach, duh! But in the years since I have made State Fair Bucks, Chicago Bucks, Arch Bucks (for St. Louis). The point is you give them fake money so you don't have to worry about them losing the real stuff. But it still gives them a visual to understand how much they are spending and how much they have left. When they want to buy something they dole out the appropriate # of beach bucks, which you swap for real bucks. It is a great way for kids to learn about money without the risk.
If you don't want to go to the time or energy to make your own money you can buy play money at the store or rob from a rarely used Monopoly set, chances are you'll be able to put most of it back when you get home.