Holiday Affair, based on John D. Weaver's story, Christmas Gift, premiered on December 24, 1949. New York City Christmas clerk, Steve Mason, played by Robert Mitchum, waits on a beautiful lady, Connie, played by Janet Leigh, who buys an expensive train set from him, no questions asked. Steve suspects that Connie is part of a shopping scheme with a rival department store and is about to turn her in. However, he chooses not to after he finds out that she is a war widow with a young son. The clerk's supervisor fires him, but he continues to pursue the beautiful woman, getting to know her young son in the process.
On Christmas Day, the young son, Timmy discovers the expensive train set under the tree, the one his mother had returned. It turns out that Steve, even though he couldn't afford it, purchased the set for Timmy. In turn, Timmy invites him for Christmas dinner. It's a complicated affair since Timmy's mother's boyfriend is also present along with her former in-laws. The two men rival for her affection. The following day, Timmy returns the train to give Steve back his money, but his request is refused when the department store owner discovers one of the cars is damaged.
A few days later, Connie prepares to attend a New Year's Eve party alone. Timmy points out that once he grows up, she will be all alone. She finally admits that she is in love with Steve and buys a train ticket for California to reunite with him.
Timmy's grandparents play with the train with him on Christmas morning courtesy http://secondsightcinema.com/holiday-affair-1949/.