Okay kiddo, imagine you saw your friend steal a toy from a store but you didn't tell anyone about it. That's kind of like misprision of felony. It means someone knows about a serious crime, like a robbery or a murder, but they don't tell the police about it.
It's against the law to not report a crime like that. It's important to tell the police so they can catch the bad guys and make sure everyone stays safe. If someone doesn't report a crime and they get caught, they could get in big trouble too.
Remember, it's always better to be honest and tell the truth. If you see something bad happen, talk to a grown-up you trust and they can help you tell the right people.