Anna (Betsy Drake) visits an orphanage and decides to foster a child against her husband "Poppy" wishes. Jane, a very unhappy 13-year-old, moves in with her, her engineer husband, "Poppy" Rose (Cary Grant), and their three children (along with an assortment of animals). As Jane's 2 week visit is up, it is Poppy who decides for her to stay as he sees how they were able to break the wall Jane had built up.
Throughout the movie, a running gag is that the Roses never get time alone.
Mrs. Rose agrees to foster a child during the summer, again against Poppy's wishes. He goes to tell the child he cannot go and finds a 12-year-old orphan, Jimmy-John, who walks with an orthopedic disability.
Jimmy-John has his wall also built and setbacks. Jimmy-John hits one of the other children, and won't speak. He is caught at voyeurism because no one would ever answer boy/girl questions for him. Poppy does. He smashes Tim's new bicycle in frustration of not being able to ride with them. It is discovered that he can barely read, and must be tutored by Anna. The Roses consider taking Jimmy John back to the orphanage, but the 4 other children "vote" to keep him.
On the night of a New Year's Eve dance, it is determined that Jane's escort's snobby mother has forbidden him to take Jane to the dance, so she attends with her brother. Poppy goes to the boys house and takes him to the dance with his father's blessing. Jane is the belle of the ball with numerous suitors.
All these setbacks are overcome and the two new children become full members of the family. Anna makes a speech to parents on the rewards of fostering older children.
The story ends with Jimmy-John receiving his highly coveted Eagle Scout medal at a Court of Honor ceremony and the Roses finally getting their time alone.