While it’s possible that poor behavior can result in a few extra push-ups, discipline is based on methods that ultimately make the child stronger/better/faster, etc.
Back in old days, many martial arts Senseis may have been harsh.  We’ve all heard the old-school martial arts stories of bamboo sticks, using pain as an influencer, and essentially whipping children into behaving.  Those are the old days and don’t (to my knowledge) exist anymore.  Judo teaches respect and discipline in positive ways according to today’s modern thinking.  While it’s possible that poor behavior can result in a few extra push-ups, discipline is based on methods that ultimately make the child stronger/better/faster, etc.  It’s not uncommon for a child who exhibits bad behavior to be assigned extra exercise, it’s all training designed to help the child improve.  Discipline is also achieved through sparring with a partner.  If the child doesn’t maintain good discipline, it’s likely they’re going to get thrown or pinned.  Improving discipline frequently results in improved focus, which are building blocks for improved performance.  Many kids walk through a Dojo’s doors to find out that bad behavior is not tolerated and that push-ups aren’t all that fun.  Ultimately, many children find ways to control their behavior, to demonstrate respect for Senseis and higher belted students.  It’s not an uncommon thing for a parent to see a change in their child’s behavior, discipline, and respect after taking on a martial art like Judo.