According to Chess and Thomas, the 2nd most common type of child, in terms of behaviors and characteristics, is:

slow to warm up

Explanation:

Child Psychiatrists, Stella Chess and Alexander Thomas, identified or classified individuals into three types of temperaments. According to many psychiatrists, temperaments are a set of dispositions or unique ways an individual responds to his environment, which are present at birth and are relatively stable as one grows. These temperaments are: easy, difficult, and slow to start categories of children.

In the study carried out by Chess and Thomas, the second most common type of children are said to be the “slow to warm up children". These children are said to be slow in adaptability, and also show a low level of activity, as they are observed to have low intensity mood in their disposition.