Yeah, but malaria mostly only kills (tens of millions of) children in poor countries in Africa and Asia so it's of no concern to right-thinking environmentalists in rich Western countries.
You're exaggerating. Malaria is a killer, but it's not tens of millions of children per year. The WHO estimates a number just shy of a million, about 50% children. That's still a sizable number and in principle you're right - most of them are in poor countries.
However, the mechanisms that drive this are more complex. A grossly simplified version goes like this: Since the population that's hit worst has no buying power, no pharmaceutical company is interested in developing a vaccine or an effective, cheap treatment. Malaria is very much a poor peoples illness due to a variety of contributing factors: No access to effective treatment, no access to mosquito nets, no proper hygienic conditions, no enclosed living spaces that keep mosquitos out.
Just spraying DDT on every swamp in Africa is not a solution to the problem. DDT accumulates in the food chain, mostly in fat and gets fed to the children you're trying to protect via the mothers milk. It is linked to an increased rate of stillborn and cancer. It's really not the kind of stuff you'd want to use if there's any alternative.
