CHERUB agents need to meet strict criteria for physical fitness and intelligence. They are usually orphans who do not have surviving aunts, uncles or grandparents (Exceptions can be made where a surviving relative is serving a long prison sentence, mentally incapable or barred from contacting their children by legal mechanism such as a restraining order).

Finding children who meet all these criteria, while simultaneously not advertising the fact that you are looking for them, has been a problem throughout the history of CHERUB. The organisation has a long standing aim to increase the number of CHERUB agents from the present level of 280 to around 400. At the end of 2003 a new measure was introduced to help with the recruitment problem. For the first time, the children of retired agents who are single parents, or who are married to another retired CHERUB, can be admitted as agents if their parents allow it.