The child wants a Milky Way. He has it in his hand, and will not put it down. Mum does not want him to have it, perhaps because he should not pick it off the display, but is happy to buy him another. She has one in her hand, and no, she will not put hers down either. The child is shouting inarticulately, and crying, and stamping his feet. The silent father looks at his son with an expression of utter perplexity. And I think, oh, that child has such wonderful spontaneous energy! How I wish I could let rip like that!
In Perelandra by CS Lewis, the main character feels rage at the Devil, who has taken over a human being and is tempting a new Eve on Venus. And he has the sense that this is what anger is for, that this anger is pure and right and this energy invigorates him.
I wonder if we stop shouting and screaming like that, in some cases, because we see how it hurts and upsets our parents, and we no longer wish to hurt them in that way. This could be out of Love for them. The child thinks, well, I like my parents actually, and there is this gift I can give them. It could also be out of trust that the parents do actually always seek my good. Developing such self control, aged 3, that one could pull back from the rage out of love and trust would be a powerful blessing. Woe awaits the child who has to develop that control out of fear of the consequences. Then the expression of energy becomes a thing to fear, he fears it could mean his own death and suppresses it. It takes a long time in adulthood to realise that such energy no longer is such a threat, and longer to take the realisation into ones heart.