A point akin to the first is this: the observation of each child should describe with great accuracy the child's relations to other children.

Has he brothers or sisters?
how many of each, and of what age?
Does he sleep in the same bed or room with them?
Do they play much with one another alone?
The reason is very evident.

An only child has only adult "copy." He can not interpret his father's actions, or his mother's, oftentimes.

He imitates very blindly.

He lacks the more childish example of a brother or sister near himself in age.