Is too much zinc harmful?
Yes. Immune function is damaged and mortality increases when too much zinc is given (Doherty, Sarkar et al, 1998). Giving generous amounts of zinc also induces copper deficiency, presumably because of competition for the DMT1 divalent cation transporter for absorption in the gut.
If you are adding 3g (half a scoop) of combined mineral vitamin (CMV) powder (from Nutriset) to 1 litre of feed, or if you are using Nutriset sachets of F75 and F100, then children will receive all the K, Mg, Zn and other micronutrients and vitamins that are needed. In this case, zinc supplements are not needed.
If CMV or Nutriset feeds are not being given, then supplement the child with zinc (2mg/kg/day), either by making an electrolyte-mineral solution or giving zinc-dispersible tablets.