> You don't want to modulo. You want to multiply the last digit by the number of children and divide by ten.

Let's see how this turns out:

     n  n * 7 / 10
    --------------
     0  0
     1  0
     2  1
     3  2
     4  2
     5  3
     6  4
     7  4
     8  5
     9  6
    

It's the same for most other numbers of children. Thanks for playing, no cigar.