Teaching is not a command going one way. It is a feedback loop in which what happens at one end changes what happens at the other. The trainer's responses shape the learner, and the learner's responses should, in turn, shape what the trainer does next.
Punishment often fails because it does not land at the same moment as the unwanted behavior. When it comes afterward, the learner can't tell which action caused it, so the lesson doesn't stick.
Getting results with a creature that cannot be forced, like a chicken, proves you don't need punishment to change behavior. Once you have seen reward alone work there, it becomes clear the same is true with a baby or anyone else. It also gives you ideas for which behaviors to reward.
There are several quite different ways to get rid of unwanted behavior, ranging from punishment or removing the offender entirely to gentler methods. The gentler ones include changing the motivation behind the behavior, or rewarding a different behavior that can't be done at the same time. Choosing among them is a matter of method, not just temperament.
The same principles of reward and timing work on any learner: animals, children, adults, or yourself. Using them is not just about being kind; it is a more efficient way to get the behavior you want. People who don't understand this end up treating those around them badly.