The 5th house corresponds to a fire sign and is therefore a house of dharma (duty of life purpose).
Children, intelligence, the mind, poorvapunya (past-life credit), speculation, gambling, sports, art of painting or drawing, morals, merit, charity, religious-mindedness, romance, love affairs, pleasure, mantras, spiritual techniques, wisdom, high learning, kingship, good deeds.
The 5th house, being a trikona (trinal house), is auspicious. The ruler of the 5th benefits whatever house it occupies. Aside from its essential rulership of children, the mind, investments, etc., it is a very significant part of a horoscope because it governs what is termed poorvapunya. This is the past-life credit (or lack of it) which is due to show up in this lifetime. Nearly all world-famous individuals have a powerful 5th house. This is the indication that they have worked hard enough to earn what is now their reward. Since poorvapunya is in a sense a "birthright", a person with great poorvapunya often feels or knows his destiny at an early age.
Also as this is the house of morals and merit, a powerful 5th denotes a person of ability, integrity, humility, and other fine qualities.
The 5th plays a major role in the lives of great saints and religious leaders since it rules religious-mindedness, morals, mantras, and spiritual techniques.
In India, marriages — at least until recently — were prearranged at birth or a young age. Therefore love affairs, as seen from the 5th, meant the quality of love received from the spouse. In the West it reveals love affairs both before and after marriage.
The karaka or indicator of the 5th house is Jupiter.
The retrograde lord of the 5th house may cause delays in childbearing, problems conceiving, or the person is simply in no hurry to have children. Usually this indicates a small number of children.
Source: «Ancient Hindu Astrology for the Modern Western Astrologer» by James Braha