The River IQ Test

This puzzle was supposedly given as an IQ test to job applicants in China. The object is to get everyone (father, two sons, mother, two daughters, police officer and thief) from one side of the river to the other while adhering to the following rules:
  1. Only two persons on the raft at any time
  2. The father cannot stay with any of the daughters without their mother present
  3. The mother cannot stay with any of the sons without their father present
  4. The thief cannot stay with any family member if the police officer is not there
  5. Only the father, the mother, and the police officer know how to operate the raft