Do kids even really know what a pimp is? If not, why would a parent dress them like one? If so, why would a parent allow them to dress like one? Why does this even exist ?
If my kid asked for this costume, there would be a big research project about prostitution in store for him. Assuming, of course, that he at least already knew what sex was. And if not, then it'd have to be couched in terms of human trafficking / slavery.