You are right there. But probably the biggest generator of orphans back then was disease. If both parents died, the children usually went with an Aunt, Uncle, Cousin, or very good family friend.
And likely picked up the new family name, no? Outside of royalty, I don't think surnames were as cherished in the past as they are now.
A bunch of my cousins are no blood relation at all, because their grandparents adopted a boy whose parents both died of the 'flu. His dad was a doctor and caught it tending his patients, and his mom caught it from him. My relations had no children of their own, so they just adopted him and I'm not sure it was ever in any official record.
I know his original birth name and have a note to that effect in my genealogy research, but it's not generally known outside the immediate family, and nobody really cares from a personal standpoint.
Another branch of the family has 2-3 instances of taking in children whose parents had died, much further back than 1918. That information could easily be lost in a century or two.
Point is, records were a lot looser back then, and many have been lost, so don't assume your ancestors were engaging in any hanky-panky. They may have been doing a noble deed instead.
>>If both parents died, the children usually went with an Aunt, Uncle, Cousin, or very good family friend.
That happened to my mom. Her mom died, then her dad got pneumonia around the same time they buried her mom. He died soon after. She was raised by her maternal uncle and his wife. My mom was around 3 at the time, so that would have been around 1938 or so.