'Abdu'l-Baha had 13 grandchildren

To catch even a glimpse of what must have transpired in 'Abdu'l-Bahá's heart when this first grandson (Shoghi Effendi) was born to Him at the age of fifty-three, one must remember that He had already lost more than one son, the dearest and most perfect of them, Husayn, a beautiful and very dignified little boy, having passed away when only a few years old. Of the four surviving daughters of 'Abdu'l-Bahá three were to bear Him thirteen grandchildren, but it was this oldest one who bore witness to the saying "the child is the secret essence of its sire", not to be taken to mean in this case the heritage of his own father, but rather that he was sired by the Prophets of God and inherited the nobility of this grandfather 'Abdu'l-Bahá. (Ruhiyyih Khanum, The Priceless Pearl, p. 4)