i'm trying to think about the child in time. i remember being annoyed by the book. i was annoyed that it didn't hold me, it was a premise, with heartstrings, that didn't hold my interest, but held my attention, like something missing. i may have missed some crucial things. well the child was missing, and never to be found, and was a child in time, but not in body, just in the mind.
the sense that you can't have it, that the child is a microcosm, even one's own, oneself, a mystery. and you can live your life trying to get back to the child, or just accept that the child past is still the mystery that lives in us.
the film, was it the second film? i seem to remember an annoying first, or maybe it was another ian mcewan, anyway this one i saw something that seemed absent from the book, a parallel child, the father/author's publisher, who after the child disappears quits the world and becomes a child again. the actor brought this man-child to life, where in the book he must have stayed flat on the page. so i saw that one child was abducted and evermore a child in time, and one had had his childhood stolen away. and he had a brief moment of captivation, in the woods he found his lost child, and the author, who lost his child, and his publisher, finds his anger in the woods watching the man be a child. spoiler. the man can't sustain life being a child. it's too late now, he knows he's out of time. he plays almost in a frenzy in the woods, desperately trying to experience what he lost. he can't, and hangs himself from his tree fort tree. and then they make another child, which seems too pat an ending, another replacement child, another attempt to keep what will continue to be lost in time. 
and as ever in art or life i sense that i have missed some essential things. and i'll just have to go on without those things, or come back to them another time, or they will come back to me.
sorry sorry sorry maybe it's annoying to watch someone try to think about time and things and childhood stuff.