Children start learning as soon as they’re born. They learn by observing those around them, what they do, how they do it, what responses occur.
Children used to be raised with their parents and perhaps older siblings, usually having a lot of one-on-one interraction with a primary adult or two, until starting school at age 4 or 5. And even that was usually only a partial day. All that exposure to an adult, who probably adores them beyond anything else in the world, gave a child excellent exposure to what is proper behavior in the real world. A great start before heading out there.
Now, kids are in day-care from infancy. Their examples are other little kids who have only had the examples of other little kids. Day care providers are loving, caring people, but it is not possible to be as attentive to 6 or 8 children, nor to give them the undivided love that a parent will. In essence, the kids who’ve grown up in daycare have grown up half wild. They can’t get that early grasp of their own uniqueness, nor that push to achieve while knowing that mom or dad is right there behind them.
I know that our society is different now. But I see families where the children actually stay within the family instead of being out of the house and in the care of strangers at an early age, and there is a marked difference.