People who have children are not disable, it is just their own desision.

If a person became a disable for his own desision (dangerous work, dangerous sport, misbehavior) - certainly, it is his own fault and he should pay himself as well.
And also should do parents who could prevent child disability, but didn't made necessary diagnostics.

Unwanted and unpredictable disability is the other case, so it is normal for society to insure these cases