Just tell the kids that you don’t trust the truck kashrus.
I used to worry when I went to the store with several little kids that they’ll consume or destroy all the attractive items that are on display at the lower level while we were waiting for the cashier. Then, I inspected the aisle more carefully and realized that these items are there on purpose to attract the children’s attention. So, I turned to simply defending the cart from kids adding items to the cart. The rest would be store’s problem.