Hey kiddo, do you know what a rule is? It's like a big important decision that lots of people agree on. The Rule in Shelley's Case is a legal rule that talks about what happens when one person gives property to another person, but they want it to stay in the family.
So let's say your grandma gives her big house to your dad, but she wants it to stay in the family for a long time. The Rule in Shelley's Case says that your dad doesn't just own the house for himself. Instead, he owns the house and whatever comes after him.
That might sound confusing, but let me put it another way. Let's say your dad has a son (that would be you!). When your dad dies, you don't just get a small piece of the house or some money, you actually get the house just like your dad did! And then when you have your own children, they would get the house after you!
The Rule in Shelley's Case isn't used much anymore in modern times, but it helped to keep property in families for a long time. Does that make sense, kiddo?