Help solve riddle

A mother, a father, two girls, two boys, a policeman and a convict are to cross the river with a boat. The conditions are:
The convict cannot be alone with any member of the family without the policeman.The father cannot be with the daughter(s) if the mother is not there.The mother cannot be with the boy(s) if the father is not there.Only the father, the mother and the policeman know how to sail the boat (so one of them should be on the boat on each crossing)The boat holds at most 2 people.