Young football players want the ball.
This is hardly a surprise. Touchdowns get the glory. Taking a handoff, or dropping back to pass, or catching a bomb down the sideline is a lot of fun. It's a safe bet that most everyone on your youth football team wants to be a skill-position player.
So how do you convince a young player to play on the offensive line?
Here's a video from a USA Football camp of a Pop Warner coach pumping up the offensive linemen at the camp. In short, he's making sure the players understand--in no uncertain terms--that it is the offensive line that makes a team go.
Once your players believe in the value of an offensive line--and more importantly, THEIR value to the offensive line--then they will be gung-ho about protecting the ball-carriers. Give it a try.