Child prostitution usually manifests in the form of sex trafficking, in which a child is kidnapped or tricked into becoming involved in the sex trade, or survival sex, in which the child engages in sexual activities to procure basic essentials such as food and shelter. Prostitution of children is commonly associated with child pornography, and they often overlap. Some people travel to foreign countries to engage in child sex tourism. Research suggests that there may be as many as 10 million children involved in prostitution worldwide. The practice is most widespread in South America and Asia, but prostitution of children exists globally, in undeveloped countries as well as developed. Most of the children involved with prostitution are girls, despite an increase in the number of young boys in the trade.