You can't prevent your child from dropping her watermelon slice on the ground (and besides, a little dirt can't hurt!), but these easy picnic pointers will help ensure the other stuff she eats is safe.
Grilled meats: Use an instant-read meat thermometer to make sure the internal temperature of steak is 145 °F and that of hamburgers and pork is at least 160 °F. Chicken and turkey need to reach 165 °F, says Bill Marler, founder of the food-safety group Outbreakinc.com. If you're a guest at someone else's barbecue and don't have a thermometer handy, ask that your child's burger or meat be well-done.
Hot dogs: Even though the package says the dogs are fully precooked, they may still carry listeria, a pathogen that can be dangerous for children, pregnant women, and the elderly, notes Marler. So cook them again until they reach 160 °F (or until they're steaming-hot, if you're nuking them). An even bigger hot dog risk, however, is choking: Cut each link lengthwise and then slice them into small bites for the little guys.
Cold salads: If you can't keep your potato and pasta salads on ice, try not to let them sit outside in the heat for any more than two hours (if the thermometer hits 90 °F or higher, throw these foods out after an hour). The same goes for deviled eggs and any dips made with mayo or sour cream.