He started his career as a merchant's apprentice. In 1677 he became a director of the East India Company, and the following year was made a baronet. Child rose rapidly in the East India Company, and in 1681 he was made its governor; thereafter he dominated the company's affairs until his death.
In 1665 Child began a series of writings on economic subjects, later gathered into two volumes, Brief Observations Concerning Trade and the Interest of Money (1668) and A New Discourse of Trade (1693). Child was only a moderate mercantilist; while he believed in a favorable balance of trade, he did not favor too much restriction of imports. He recognized that his country could not continue selling to others without buying from them. He particularly advocated a relaxation of the Whig government's restrictions against French goods. On the other hand, the laissez-faire attitude did not extend to the British colonies, with which he thought England should have a monopoly of trade; nevertheless, he could hardly espouse any other belief while his personal fortunes were bound up with the East India Company. Child's most important influence, however, lay in his strong advocacy of lower interest rates, which he urged the government to establish as a means of stimulating business activity. In this respect he anticipated more modern ideas on the control of depressions. Child also vigorously opposed restrictions on the export of gold and silver bullion, contending bullion was a commodity like any other.