Hey there!
The answer is 4. the average number of school-age children in families sending a child to the day care center.
All of the other things would be important to the analysis.
Unless the daycare has some sort of after school program as well, there would be no need to know the average number of school-age children in families sending a child to the day care center because the school-age children wouldn't be involved in the day care center. They would be at school during the day, and therefore wouldn't need day care.
Hope this helps!