I have totally thought about this a bunch because the implications are fascinatingly squicky. Obviously they couldn't be Hogwarts students because they'd be recognized by professors or friends or could even run into themselves, etc. They can't be wizarding children from Hogsmeade because they'd be too young to blend in. (One of the girls is described as a first year but the rest are older, if memory serves.) So either Draco is going into the Muggle world and TOTALLY STEALING bits of hair, etc, from Muggle children, or there's a black market for this.

The real issue here is that OBVIOUSLY Draco would make girl!Crabbe and girl!Goyle have sex with him. I mean, honestly.