Sabrina came out before the MPAA rating system got going in 1968, so it doesn't have an official rating.
Still, it's clearly an all-ages endeavor. It's almost tame enough to get a G, though director Billy Wilder slips in some sexual innuendo. (David pretty clearly has casual, extra-marital, off-screen sex with Gretchen Van Horn, early on. Naughty David.)
The other bit that could be mildly disturbing for children is Sabrina's suicide attempt early on—though you could also see it as a kind of public service message: don't shut yourself in the garage and turn on your car, kids. As Linus says, "Haven't you ever heard of carbon monoxide? It kills people."
However, if you want to shield the young people in your life from truly fantastic mid-century French fashion, keep them away from Sabrina. It might scar them for life… or at least tempt them into paying the big bucks for an all Givenchy wardrobe.