By the 1820s, many people began to believe that childhood cruelty to animals would inevitably lead to adult cruelty to other human beings. Encouraging kindness became an important part of raising children. Advice books for parents, Sunday-school lessons, children’s books, prints, and other objects all reinforced the importance of kindness and the cost of cruelty.

Advocates of kindness to animals used four metaphors to compare pet animals to people. They argued that animals were like humans in being loyal servants, loving parents, childlike innocents, and true friends. Because of these good qualities, animals were entitled to loving care. Stories, poems, and pictures representing these ideas became popular in the nineteenth century. By the 1820s, pet animals and children were often depicted together as playmates and friends. The word “pet” was used for both children and animals.