You're referring to the first sentence of the Childhood section. The first source does say 1835, but this is inconsistent with the text in the lede and the infobox, which say 1828, and I don't believe that source is reliable. (In fact, it looks as if there are several unreliable sources used as refs in this article.) The snippet from the second source implies 1830. The third source (actually just a footnote) suggests there's uncertainty. If no one can provide a good source giving a firm date, I suggest the article should note that the year is uncertain.