Adoptions were not documented back past say a 100 years ago.
That's been my thought. After wars, plagues, etc. there must have been many orphans. Maybe people would then just take in some kid or maybe a religious official would arrange for that. There would be few if any records of these adoptions. Makes sense to me, anyway.
And then there are the rapes that accompany societal upheavals. And the prostitution for survival.
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.