1. Write a letter to themselves. Tell their ages, who their friends are, favourtie TV show, song, book etc. Write about what's going on. Tell their future self about how they feel. Talk about what they would like to be when they grow up and five things they want to do when they grow up.
2. If it's safe to get a newspaper, get one and cut out articles that they think would be important to their future self. Or print them from online.
3. Draw a picture of their family as it is now.
4. Take some pictures of today, print them out and include them in the box.
5. Put it all together in a scrap book or a lunch box and store it somewhere, like a loft, where you will not come across it for years to come!