Unlike his legendary great-grandfather, Louis XIV, Louis XV was not a dedicated father to his illegitimate off-spring. That in itself is quite strange since the King was an adoring father to the children he had by his wife, Marie Leszczynska.
Of the many illegitimate children fathered by the King, there was just one who was actually officially recognized: Louis Aimé de Bourbon. But not even he was to go on and have a brilliant court career - instead he became an Abbot.
Rather than living at court or being married into families of the nobility, a different kind of life awaited the children born on the wrong side of the sheet. The method adopted by Louis XV was to have the paternity listed as a non-existent person; occasionally both parents were made up. However, the King did make sure to at least give these imaginary parents somewhat decent ranks but never one that would arouse suspicions.
Another thing that is odd about Louis XV and his bastards is that he seemed to have had very few of them by his actual mistresses. Neither one of his most famous mistresses, Madame de Pompadour and Madame du Barry, had children by the King. From what we can tell most of his bastards came from women he never recognized as mistresses or perhaps even only had brief liaisons with.
Because Louis XV never had his children registered - officially or unofficially - it is unknown exactly how many he had. An estimated guess is around 15.