A stroller is a small carriage with wheels meant for pushing a baby or toddler around. For a baby, there is no better ride than a stroller.
There are two main meanings of the noun stroller: a person who strolls, and a parenting appliance that to many English speakers in the world is called a pram or a pushchair. A long-forgotten copywriter at Sears & Roebuck is probably responsible for the latter meaning; its first appearances are in the catalogs of that company. As for stroll, the underlying verb: it's a German import, though ultimately of uncertain origin.