How much spending money should I plan on having for 3 day vacation?

I am taking my children to the Delaware coast for three days. We are driving and staying at a campground, which are both money saving options. We can cook hotdogs there, but realistically if we are on the beach/boardwalk for three days, I will end up buying food and spending money. There is a candy store, an arcade, ice cream and probably many little stores to shop in. We haven’t gone anywhere besides on planned and organized camping trips and so I don’t know how much money I should plan on bringing. Oh and my husband is coming too, so 2 adults and 2 kids.