Mutually acknowledged relationship of parent and child; stepchildren

The transfer of property passing to any child to whom the decedent for not less than ten years prior to such transfer stood in the mutually acknowledged relation of a parent, provided such relationship began at or before the child's fifteenth birthday and was continuous for ten years thereafter, shall be taxed at the same rates and with the same exemptions as the transfer of property passing to a child of said decedent born in lawful wedlock.

The transfer of property passing to a stepchild of a decedent shall be taxed at the same rates and with the same exemptions as the transfer of property passing to a child of said decedent born in lawful wedlock.

This section shall apply to the estate of every decedent, whether the said decedent died prior to June second, one thousand nine hundred and thirty-seven, or shall die after said date, but this section shall not entitle any person to a refund of any tax paid prior to said date.