There were a couple of ways that photography studios could take photos of very young children & babies, depending on how old they were & how well they could sit unassisted. The kids could be held by a parent, left in a buggy, pram or stroller, propped into the corner of an over sized chair, squeezed into a small chair, or held in the lap of a parent that is covered by a blanket or piece of material.
Late 1800s-early 1900's real photo postcards made from more candid images of real people. Not models & not in a studio. The top card is French, the others are American.