Just a loose thought I'd like to share. Would love to hear those who disagree:
Assuming no birth control takes places - the poorest regions have also the highest population growth already and helping them would lead to more of the same, amplifying original problems of those regions creating bottomless well of help.
As KHorton has alluded to, there is a well-established body of literature which indicates that development leads lower Total Fertility Rates. Examples include the books Common Wealth by Jeffrey Sachs and Factfulness by Hans Rosling et al. The following online resources also explore this:
As you've said, I wouldn't say "the best way to reduce population growth is providing malaria nets". But I would say "I don't think malaria nets will cause a major increase in population in the long term".