Let f be the number of families.
If f = 2, the minimum possible number of girls and boys is 3 and 4.
Thus, number of children = 3 + 4 = 7 and number of adults ≤ 4
But as adults can be equal to boys, f cannot be 2.
If f = 3, minimum possible number of girls and boys = 4 and 5.
Thus number of children = 9 and number of adults ≤ 6
This is possible. Thus the minimum number of families in the locality = 3.
Hence, option (d).