If my child eats the dog's food, what should I do?

Make sure... ...The dog does not starve. Dog food is not toxic to humans, and is in all probability less harmful than much of fast food, sweets, and processed snacks children may find in the "impulse buy" section of the supermarket. If the dog dish was contaminated with dog feces, diarrhea or worms are possible, otherwise that's not a major concern.
Dont worry. Many children eat dog or cat food. These days it is often as good or better than some of our human foods. The only worry i would have is if the child is taking it from the dog and the dog is growling....Otherwise...No worries. Keep the food out of child's reach if you can and teach him/her to respect dog's space when eating.