It's not okay to steal from othes.
Frank sees Ken riding around on a new bike he got while he is still using the one he got 10 years ago.
Frank wants a newer bike.
Frank decides to ask his parents for a new bike since his old one is now far too small for him.
Frank pushes over Ken and takes his bike and rides away on it.
Frank is surprised when his parents agree and actually get him a new bike.
Frank gets grounded for a month for taking someone else's bike.