Some normal bikes do have a limited range of seat-post and handlebar adjustment. Raising the seat-post has very little affect on the reach to the handlebars, resulting in a cramped cockpit that is awkward and uncomfortable to use.
LittleBig is different, the actual frame grows, meaning it can cover a much wider size and age range. In addition to its unique growing frame, LittleBig has all of the usual saddle and handlebar adjustments, meaning you can fine tune the fit for optimum comfort.