While I agree with you that we should not unnecessarily try to criticize the Zulu nor add things which are not related to the article I still believe that it is an important part of the background story which leads up to the battle, it basically lets the reader know that these Boers knew that the Zulu would not show mercy to even the most innocent ones among them. Dingane wanted the Boers out of his territory using whatever means necessary which did not stop short of brutally murdering infants.