Okay, so imagine your favorite superhero, like Spider-Man or Batman. When they do great things, people might keep things that are associated with them as special mementos or souvenirs, like a piece of their costume or maybe a gadget they use.
Now, Sariputta and Moggallana were two very important people in Buddhism a long, long time ago. They had very special abilities and did lots of important things for Buddhism and its followers. When they passed away, people kept special items that were associated with them.
These special items were called relics and they were things like pieces of their clothing or bones. People believed that these relics held special power and were important because they were connected to Sariputta and Moggallana.
People would keep these relics in special places like temples or shrines and they would go there to pray and ask for good luck or blessings. It was like having a special superhero object that would protect them and give them strength.
So, even though Sariputta and Moggallana are not around anymore, people still keep their relics as a way of remembering them and feeling connected to the special powers they represented.