When I lived in Japan in the 1970s, strollers were rare, and children who were too young to walk were carried on someone's back, usually the mother's, but sometimes a grandparent's or older sibling's.
I returned after an 8-year gap to find that carrying babies onbu-style was nearly extinct. Visiting my old neighborhood, I noticed that an acquaintance was carrying her "afterthought" child (about ten years younger than the next one) on her back, and when I remarked on the fact, she said that most young parents preferred sutorooraa or sunaggurii.