This movie got poor reviews (37% on the Tomatometer), but it's really not that bad. Maybe it's that movie critics tend not to be parents of small children, and haven't recently had that sinking feeling of losing track of a kid.
That's what happens to Jodie Foster here, and it happens, of all places, on a transatlantic jet flight. And unfortunately, the other passengers and flight crew soon have their doubts whether the child was on board at all. Nobody seems to have noticed her except Jodie!
Jodie Foster is a fine actress, and the other cast members are pretty good too. To go into detail would require major spoilers here, but the real problem is that the plot becomes more and more farfetched the more you think about it. Well, that understates things: it becomes completely unbelievable. (If you're so inclined, check the IMDB message boards where they fly jumbo jets through the plot holes.)
But it's pretty easy to suspend disbelief while watching the movie; things move along at a decent clip once the child disappears.
I guess when you make a movie like this, you're pretty much giving up on selling it as an in-flight movie.