The third theory, which is perhaps less prevalent than the others, Freud terms the sadistic theory of coitus.

The child realizes that his father must have taken some sort of part in his production.

The theory that sexual intercourse consists in violence has in it a trace of truth, but seems to be arrived at rather obscurely.

The child's own sexual feelings are often aroused for the first time when wrestling or struggling with a companion; he may see his mother, also, resisting more or less playfully a sudden caress from his father, and if a real quarrel takes place, the impression may be fortified.

As to what the state of marriage consists in, Freud finds that it is usually regarded as a state which abolishes modesty; the most prevalent theory being that marriage means that people can make water before each other, while another common childish theory is that marriage is when people can show each other their private parts.
Thus it is that at a very early stage of the child's life we are brought face to face with the question how we may most wisely begin his initiation into the knowledge of the great central facts of sex.