Really, not the kind of story that bears telling via the film medium. Skip it and spend the money on the book instead.
This is a book with many characters, and I love it for how crowded it is. I love how characters are differentiated, how they react to events and situations unpredictably. Byatt has succeeded in creating several interesting roles, which inspire a variety of emotions in the reader: Olive Wellwood, an author of children's tales, beautiful, unrealistic, somewhat weak, inspires a fair amount of irritation; her philandering husband Humphrey, father to many women's children, is alternately disgusting and charming; Herbert Methley, advocate of free love, is sly and frightening; Elsie Warren, a young woman who falls prey to Methley, generates empathy for her innocence and admiration for her subsequent independence -- and so on.
The Children's Book follows the life and times of several creative, talented, offbeat adults in the late 19th century, and studies the impact of their choices on their children and the paths the new generation chooses for itself. In terms of plot, it is a success, though I personally feel it extends too far into the 20th century and there was not much need to include a wartime dimension. But it is so heavy and ponderous in the telling that the pleasure in reading seems to leach out about halfway through, especially after a painfully detailed and uninteresting description of the "Grand Exposition Universelle" at Paris, where Byatt insists on painting a verbal picture of every statue, every tent, every puppet and other conceivable artistic work displayed there.
But if you can manage to tolerate/skip the boring bits, the 600-page read is worth it for the richness of the characters. Anselm Stern, the German puppetteer; Julian Cain, intelligent, weak, confused about his sexuality; Dorothy Wellwood, who fights the prejudices of her times to become a doctor; Benedict Fludd, a wild, deranged artistic genius -- and many, many more. Be warned that it will take time and effort to make it through the whole book, though, and that the prose is patchy and sometimes even yucky (a young boy masturbating is described as "working himself into... a soaring wet ecstasy") but Byatt manages to achieve a compelling study of human nature, even if the free history lesson is quite unwanted.