It's worth noting, though, that deworming 200-1000 children doesn't mean deworming 200-100 children who have worms. It means administering deworming medication to 200-1000 children, a few of whom will benefit (because they had worms) and the majority will have no effect (because they didn't). IIRC, programs like Deworm the World don't target infected children, because figuring out who to treat is more expensive than just treating everyone, if you're in an area with a high infection rate.
Overall, it might still be more effective than GiveDirectly, but it's not as simple as "this would directly benefit 200-1000 children rather than one family". (I'm not saying that's what you were saying, but that's how I would interpret it if I weren't familiar with the programs.)