Okay kiddo, let me explain what a donativum is. Imagine that you have a toy that you really like and you want to give it to your friend as a present. This is kind of like what a donativum is, but instead of a toy it's something more valuable like money or property.
When someone gives a donativum, they are giving a gift to someone else without expecting anything in return. It's like when you share your snacks with your friends during snack time at school. You don't expect them to give you anything in return, you just want to be friendly and generous.
These types of gifts can be given for many different reasons, like when someone is happy, grateful, or just wants to help someone else out. For example, imagine that your grandma gives you money for your birthday. She's giving you a donativum to show how much she cares about you and wants you to have something special.
Now that you understand what a donativum is, remember that it's always nice to give gifts to show how much we care about someone else. And sometimes it's just fun to make someone else happy!