Malaria risk for kids???

If you go to the community tab on this site (expat.com) you will see a listing for blogs. Take a look at some of those as many are written by mothers who are expats living in TZ with their young families.  From there you may be able to contact them directly with your questions. I have also found some wonderful blogs about TZ expat life while on Pinterest - typed something like Arusha TZ in the search criteria, and maybe even tried expats TZ - don't recall know what I used but you can play around with different search requests and you will definitely find info.  Also using similar search criteria in Google will get you all kinds of information.  Another thing you could try would be to google (for example) international schools arusha TZ (or Dar or wherever), and once you have those you can go on their site and find a lot of information about kids, health, activities, etc, and at least have a point of contact for your questions who may in turn be able to direct you to someone specific.
I have become the research queen these days as we are working on our move To Arusha a bit later this year.  Lots of info out there - you just have to get a bit creative in your approach to track it down.
Best of luck!