IIRC, Aunt March is the girls' great-aunt -- Mr March's sister-in-law. Alcott calls her "childless" early on and says she offered to adopt one of the girls when the family lost their money, but later on when Amy looks at her treasures they include "baby bracelets" her one daughter wore. But the pearls her father gave her on her wedding-day are to go to the first bride in the family, so maybe if she had a child it died early, I don't remember.