A good breakfast and a healthy, nutritious school lunch are very important for school age kids but so is a healthy after school snack, especially if they have a little home work to do before dinner.
These snacks don't have to be too complicated - simple things like sliced apples or celery with peanut butter and raisins or dried cranberries or graham crackers with cream cheese and fresh blueberries or sliced strawberries, or both, with a glass of juice on the side are good ideas.
You could make slightly more substantial snacks by making mini grilled cheese sandwiches or toasting a multi-grain waffle and serving that with peanut butter or chocolate hazelnut Nutella with sliced bananas on top and a glass of milk on the side.
The possibilities really are endless, you just want to keep things on the healthy side and make sure they're not too filling so that, at dinner time, they'll still want to eat a healthy meal.