Each year hundreds of unlabeled personal belongings end up in our lost and found that are not retrieved and have to be donated or disposed of. Water bottles, lunch boxes, backpacks, jackets, sweatshirts, sneakers, sports equipment and other items should be labeled with your child's first and last names.
A laundry marker may do it, or you can see this article for more ideas: The Best Labels for Kids Lunch Boxes and Clothing.