Baby food texture. Products that are firm enough for the child to pick up as a "finger-food" but which quickly soften upon contact with saliva are the best bet. Arrowroot cookies and the newer "puff" products seem like good choices for this age group. One must be with baby at all times and monitor each individual baby's tolerance of increasing texture.
Non Choking. The risk is choking. There is no biscuit truly safe unless it is in very small peices and very soft so that it dissolves in the mouth without chewing.