Where child living when will made

If a will be made when a testator has a child living, and a child be born afterwards, such after-born child or any descendant of his if not provided for by any settlement, and neither provided for nor expressly excluded by the will, but only pretermitted, shall succeed to such portion of the testator's estate as he would have been entitled to if the testator had died intestate, toward raising which portion the devises and legatees shall, out of what is devised and bequeathed to them, contribute ratably, either in kind or in money, as a court in the particular case, may deem most proper. But if any such after-born child or descendant die under the age of eighteen years, unmarried and without issue, his portion of the estate, or so much thereof as may remain unexpended in his support and education, shall revert to the person or persons to whom it was given by the will.