@YouDNewb:
It seems he says its Candy but its actually the experimenting substance, just disguises as candy so the kids will eat it
After I re-read the chapter Im pretty sure the candy is just a way to keep the kids from fleeing.
@King:
The candy is both. It has a stimulant put on it (NHC10) that makes the children grow and get addicted to it.
At least that's how I understood it.
Again I re-read the chapter and Chopper(Sanjis body) thought they were giant kids even after he had identified NHC10 in their blood. That pretty much confirms that the candy was just to addiction bind the kids so that they couldn't escape.
@sag:
This is a simple yet highly relevant question. As I see it the first proposition is a given but the latter one might as well be possible;however, if there's another substance in those candies that can stimulate the pituitorial gland then Chopper either missed it or he doesn't know its existance, although I see this highly unlikely.
On a side note, the children stated they had "check-ups" but we've got no information about the procedure is followed during said sessions. So theres a chance that the "medecine" responsible for the children riculous growth rate is somewhat suministrated during said check-up sessioms.
The conclusion I came to^^