Depends on the time period, and honest we simply didn't have modern medicine either. Your disabled child might have been left on the streets, left in the woods to die, or sold to someone else (other children might have been sold too). An infant? Infanticide was a thing at different times. Sometimes you'd be sent away to a home, where you'd be abused.

You were often an outcast and a beggar and your life was a lot worse. And even worse, folks might have treated you like you deserved it because it was a sign of god's wrath.

In short, folks with disabilities have it better than they did in the past because we started banding together as a society and taking care of folks (government). And we still fail folks.