What was an effect of the Black Plague on families?

The death rate dropped.

Infant mortality rates decreased.

Individuals were able to marry at a younger age.

The birth rate decreased.

I believe the answer is: Individuals were able to marry at a younger age.

The black plague increase the death rate among young adults to middle age people at that time. Because of this, many of them decided to marry and procreate at a younger age because they fear they would not be able to do it in the following years.

It's obvious. Black Plagues took many lives, so the answer is the last one: The birth rate decreased.