I surely am glad there were at the time no activist judges in Minnesota.
A child belongs with his parents or parent regardless unless they are proved morally, intellectually or mentally unfit to raise the child. Throughout most of history girls (women) had children beginning at age 14 or 15 in and out of marriage. No one ever claimed they could raise these children better than the parent or parents.
Your Grandmother was still living in the same house with your children.
That was a time when a new mother had support from everyone in her family. They may not like what she did, but they were always there to help with her new child.