Kevin is six years older than his twin sisters. The sum of the three children's ages is the same as their 42 year old dad's age. How old are the children?

Let the age of Kevin be x,

age of twin sisters = x - 6

sum of children's age = x + x - 6 + x - 6

= 3x - 12

3x - 12 = 42

3x = 54

x = 54/3

= 18

age of twin sisters = x - 6

= 18 - 6

= 12

Kevin is 18 years old whereas the twin sisters are both 12 years old.