No 'how many' is involved. The dictionary definition of the word 'holocaust' is "complete destruction, usually by fire". In this context it has another meaning; the attempted extermination of the Jews by the Nazis. There are no "a" holocausts, just the holocaust. The Palestinian conflict is not "a holocaust". Neither is that in Darfur. Nor were Rwanda or Cambodia, just to name two. That makes no judgement on how 'bad' those events were.. all were (are) terrible events and appalling human tragedies.

The problem is not just sloppy use of language. It is a deliberate distortion of that language to make a political (not a humanitarian) point (can you provide a link to the "Darfur holocaust memorial museum" please?). It is using dead children for that purpose. Use of the word 'holocaust' turns the museum from a memorial into propaganda. As I said, it insults the dead of both conflicts.