This phenomenon is called Lithopedion, which means “stone baby”. It occurs after an abnormal pregnancy and death of the fetus, when for some reason it is retained by the mother’s body. The fetus is too big to be reabsorbed, so it gets calcified by the mother’s body, to shield her from the dead tissue. This is extremely rare (Source)
-Our 2ft Kobold fighter who can already use a 6ft greatsword with ease