ok, here's the solution, in 17
steps. not sure if i can eliminate any steps yet.
1. policeman and thief go across
2. policeman comes back
3. policeman and boy #1 go across
4. policeman and thief come back
5. father and boy #2 go across
6. father comes back
7. mother and father go across
8. mother comes back
9. policeman and thief go across
10. father comes back
11. mother and father go across
12. mother comes back
13. mother and daughter #1 go across
14. policeman and thief come back
15. policeman and daughter #2 go across
16. policeman comes back
17. policeman and thief go across.
A true lover of nature does not despair now that his mistress has turned a colder cheek.