... but that really isn't the issue in this episode.
Beaver has a brand new bike with lots of features, and his friends have begun riding their bikes to school. Thus Beaver asks for permission to ride his own bike to school. Ward and June relent and agree, making sure he has his lock to secure the bike and making sure he knows not to dawdle either on the way to school or back home. But no parent or other mere mortal can protect against the bad company of Larry Mondello!
The first afternoon on the way home, Beaver and Larry are looking in store windows on Main street when a kid comes up and compliments Beaver's bike and asks if he can take it for a ride to test the gears. But the kid never comes back. Now Larry urged Beaver to let this kid ride his bike and made it sound like he knew who the kid was, but in fact he was a stranger, and ultimately Beaver is responsible for his own actions.
When he gets home his dad loses his temper over what he did, and they call the police. But it turns out Ward made some mistakes too. He didn't register the bike with the police so they can more readily identify it (today they'd probably tax it too!). He also didn't get the bike covered with his insurance company. His own costly errors make him more forgiving of Beaver's.
A humorous aside given future events - At one point Beaver describes the kid who tricked him and stole his bike as a "crook". June chides Beaver, asking him if he would talk to the president this way, using the word "crook". Oh, June, I know it is only 1960, but just you wait!