I agree, because by being disciplined you knew not to do what you did again because you knew the consequence.

Exactly. They will give them fear to not do it again. So they will avoid doing it.

Yes, because then they wont do what they did in fear of getting spanked again. Since they will know the consequence. Although, there is also a line a parent shouldn't cross such as the appropriate spanking and abuse line.

I believe the baby should stop at 3 months. By the kids age on the cover, he looks like he should be drinking out of a milk carton.