Pretty much what Helen said. A creole is a nativized pidgin, and a pidgin is a simple artificial language for elementary communication (link and link. Though saying that children create it makes it sound too volitional. The pidgin in the mouth of babes changes and develops to become more complex grammatically. Tok Pisin (link and link) is a New Guinean creole which has been studied extensively. At least one linguist, Theo Vennemann, thinks that Germanic derives from a non-Indo-European-based (or Old European) pidgin that developed into a Creole. IIRC.

Ceci n'est pas un seing.