Boundary testing

Mingo loves drumming since he could hold the drumsticks. He starts to engage in the drumming movements after he was 18 month. It seems to give him a way to unleash his energies. I often feel a sense of peace after he finishes drumming. 
        
About two weeks ago, he turned to 19 months and a half. One night,  I was trying to assemble a piano model on the floor beside him, while Mingo was engaged with a coin game. Out of nowhere, he suddenly came to me and hit my head with his hand. I told him that "when you hit me, I am sad because it hurts." Then I pretended to cry. He immediately came to me and touched my head gently. I stopped crying and told him that "thank you for showing your empathy. I am okay now." Usually, this will be the end of story. 
        
Somehow that night it was not how it ended. He saw me stopped crying and then raised his hand to hit me again. This scenario repeated couple times that it became a game. He was having fun watching my dramatic reactions. I decided to take a different approach. When he tried to hit me again, I caught his hand and told him that "touch me softly." The same time I was guiding his hand to touch my face softly and slowly. When I released his hand, he quickly raised one hand and tried to hit me again. I caught the hand, and there went another hand, attempting to hit me. I grabbed both hands and told him with a kind and a firm tone, with my eyes looked into his, announcing that "I don't like to be hit. Touch me softly please." Then I put his hands gently on my face, and let go of his hands. The scenario went on and on repeating itself in a circular pattern. I started counting. He tried to hit me 20 times before give up trying. I caught his hands 17 times. His hands were as fast as cat's claws. Have you ever watch how cats fight with their claws?
        
I felt it must be fun to watch the whole scenario. There was this urge of hitting from Mingo, almost like a basic instinct that just developed. The second day, he tried to hit me five times with his hands. The third day, there was no hitting. He pretended a hitting action towards me, but he could leave a space between his hand and my body. Then he looked at my face for confirmation. I told him, "yes. Mommy doesn't like to be hit." And then he left to play something else.
            
The next day, when he was drumming at night, he came to hit me using a drumstick. I didn't catch it the first time. As it didn't hurt, I told him peacefully that "I don't like to be hit by drumstick as well. Drumstick is for beating the drum." There he was, in between the drum and me. He went back to the drum, and hit the drum with the drumstick in one hand, and then came back, trying to hit me with the drumstick in his other hand. I caught the drumstick and repeated my message. There he went on repeating this process for about 4 to 5 times. 
        
Interesting enough, that I could feel that the strength trying to hit me got lighter and lighter. In the end, it almost felt like a feather. I still told Mingo that "drumstick is for drumming." Then he gave me the drumsticks. I hit the drum a couple of times and invited him to do drumming. He came to get the drumsticks with an awkward posture, to show his unwillingness. But he grabbed the drumsticks and started to hit the drum. It only took him 10 seconds to engage himself into drumming, and there he continued for almost 10 minutes. He also invited me midway to watch his play. 
        
Now it is about ten days after this event. Mingo hasn't done any hitting since after. I feel that the drumming incident was a realization point for him that hitting mommy is not okay. 

It is interesting that moms of the same preschool class have shared similar behaviors of their children, not hitting but biting. I am wondering if there are essential human functions embedded within children, that one day they suddenly feel the power to do something, and they just do it. 

Children don't know the boundaries of the world. How would they know? They didn't come with instructions of how to function properly in this world. When they feel the restraint, they test it. Psychologists suggest that the learning mode for children from 18 to 24 month old is through trial and error. They need to explore different options around the restraint to understand what is acceptable, and what is not. Then, they start to internalize the boundary. Once the child realizes the limit is firm and consistent, he or she gets the sense of security. He or she accepts it as a fact, and he or she moves on. Is this how our brains start to generalize? I am curious.