Remember that children love to get out and play and sometimes will eat very little so they can have more time on the school playground. Packing a snack for early or late recess may be a good idea (peanuts and cashews are full of fiber and protein). Don't be upset with them if their lunch is only half consumed. She is just a social butterfly. Offer sliced peaches and plain yogurt when she gets home. Make a fruit smoothie with your son using frozen fruit, vanilla yogurt, and milk.
Talk to your child about the lunch program and help him choose a healthy option. Although it is quite convenient not to pack a lunch, try a bag lunch at least two times a week. For older kids this can help your budget as kids who can go off campus can spend a lot on lunch (of questionable nutritional value).
Healthy things to pack:
Edamame (soybean) or sugar snap peas (good source of protein)
Cube cheese and offer it on a toothpick
Trail mix (nuts, dried cranberries stick pretzels)
Sliced mango, kiwi, or apples (use orange juice to help prevent browning)