Prosecutors have taken the rare step of charging a motorist with manslaughter in the death of his 6-year-old son in a car crash because the boy wasn't wearing a seat belt.

"The point is to be made to all parents that it is your responsibility that your child is seat belted in - no matter how much they fight, kick, scream," said Pamela Davis-Springer, deputy district attorney.Walter G. Sylvia Jr., 49, of Acton was driving his son, Michael, to school Aug. 8 when he lost control of the car on a winding road, authorities said. The car flipped twice, and the boy was thrown out. He died about an hour later.