So here are some facts to help you in your decision:
Consider the nutritional value of a PB & J made up of two slices of Roman Meal wheat bread, two tablespoons of Jif peanut butter and two tablespoons of Knott's Berry Farm Strawberry jelly.
Calories from Fat: 150
Based on the Recommended Daily Intakes for kids 4 and up (for all the details see here),
this means that one PB & J satisfies approximately 27% of a day's fat, 23% of a day's sodium, 24% of a day's carbs, 16% of a day's protein, and 13% of a day's fiber.
Take into consideration that your kids also had PB & Js for breakfast and lunch making an entire day of PB & Js coming pretty darn close to fulfilling the Recommended Daily Intakes AND add in the fact that a typical American kid will consume approximately 1500 PB&Js by the time they graduate high school, and all of sudden, that 5th dinner comprised solely of a PB&J doesn't sound so bad. It sounds like the right darn thing to do.
Serve it up.