This film is the credited screen debut of Margaret O'Brien, the title character, and also stars Robert Young, Laraine Day, Fay Bainter, and Nigel Bruce. It was directed by W. S. Van Dyke.
It begins with an American reporter (Young) and his pregnant wife (Day) arriving in London from war torn Europe. They've been chased out of each country invaded by the Germans as they fell, with Young writing a column about the events for Bruce, presumably the paper's editor. Young wants his wife to return to the States before the baby is born, but she wants to stay with her husband as she has thus far.
London, of course, is under attack from the Germans daily and each man is assigned a number, an area to look for survivors in the rumble when his area is bombed. Bruce and Young both have the same number which is called various times so that the film makers can show the horror of living in an environment which is bombed every night, and lots of special effects too. Young also goes out most evenings looking for human interest stories, and one night he helps rescue a boy named Peter (William Severn), who has a stuffed animal lamb which Young inadvertently pockets.
Because the hotel's basement bomb shelter is full, Young and Day have to sleep in the 3rd floor corridor. One night, while Young is out, their hotel is bombed and Young returns to learn that Day has been taken to the hospital. He learns from the doctor that she has lost the baby and can never have children again, but that he shouldn't share this last fact with her until she's more stable. However, several months later and knowing it anyway, she must return to America to recover further because she and Young have been spiraling down emotionally, and salving it with alcohol. Their friend, Bruce, who has noticed the changes (especially in Young's writing) is worried that they shouldn't be separated, but she leaves anyway.
Bruce then assigns Young to write a story about Trudy Strauss (Bainter) and her home/school for orphaned children. Though he is reluctant at first, he accepts the assignment and finds Peter already at the school. He remembers the lamb he found in his pocket, and has it returned to him. While there, Margaret is brought in, back from a foster mother who can't deal with her and her crying, which the mother has been stifling. Strauss and her staff allow her to cry (something O'Brien does on cue particularly well) and help her to get settled in. Though Young wants to leave by this time, Strauss persuades him to stay and he, along with Peter, help Margaret come out her shell. In fact, Young makes a connection with both of the youngsters, giving them baths and putting them to bed, such that both claim him as their own.
It's not really hard to tell where the story is going at this point, given the title of the film and the fact that Young's wife is recently childless. However, how "it" gets there does involve some interesting negotiations and, of course, sentimental moments worth watching.
