The way I was taught to read playing cards, Queens and Kings are often real people, representing women and men respectively, while Jacks are only rarely real people, although the Jack of Hearts can represent a real child.

Jacks tend to represent news and attitudes.
The Jack of Hearts, in addition to representing a child, can represent someone or something who is fresh, naive, immature, honest, happy-go-lucky. In love readings, for instance, it tends to show flirts and situations that haven’t fully matured yet. It is also a card of inexperience.

The Jack of Clubs represents friendship and help. It represents also service to others. Next to another court card representing a person, it shows that he or she is helpful, friendly, positive, serious, constructive. The card is also connected to cooperation and, as an extended meaning, to co-workers.

The Jack of Diamonds represents messages and the knowledge of facts. It shows the acquisition of information. As an extended meaning, it signifies study and research. It can also signify a go-between (you will notice that the Jacks of Diamonds and Clubs are similar to their Sibilla counterparts). The card points to someone who is inquisitive, curious and desirous to delve deeper into something.

The Jack of Spades signifies enmity. It shows a negative attitude toward the querent (or of the querent toward someone or something). It is a card of ill-will. It is also the uniform card, especially when together with the King of Spades. Animosity, a competitive attitude and the desire to dominate another are all part of the meanings of this card.

Despite the Jack of Hearts being the Child card, all Jacks can represent children. Usually, the Jack of Spades is a child with problems, or a sick child, or a child that misbehaves. The Jack of Clubs is a good child, while the Jack of Diamonds is a smart child.