Now If Only Britney Had Been At The Wheel . . .

When advocacy groups get ghoulish:

Two Staten Island girls who survived a 300-foot minivan plunge that killed their mother were strapped in the vehicle — highlighting the importance of seat belts and child safety seats, officials said yesterday.

The Han sisters — Etana, 3, and Ariana, 5 — suffered minor bruises in Wednesday’s accident at Bear Mountain State Park in the Hudson Valley.

Park Police Lt. David Love said Etana was strapped into her car seat and Ariana was wearing a seat belt when their minivan rolled off a cliff.

The girls’ mother, Hejin Han, 35, was in front without her seat belt on and was killed.

“It is a sad family tragedy. However, it shows that safety seats are extremely valuable to protect children,” said Stephanie Tombrello, executive director of SafetyBeltSafe U.S.A., a child-safety advocacy group.

“The fact that these parents took the time to strap their kids in is what saved them,” Tombrello said.

The only mistake, Tombrello added (well, with the notable exception of driving off a cliff in the first place), was that the five-year-old should have been in a booster seat:

She said the 5-year-old should have been in a child booster seat, “but clearly that safety belt did its job.”

She recommended that children ride in rear-facing car seats up to age 20 months to better protect them from frontal and side crashes. She also suggested that kids up to 80 pounds ride in booster seats.