There have been probably thousands of Christmas movies, specials and TV programs, many of them for children, but relatively few have an overt religious theme. "A Charlie Brown Christmas" is a notable exception.
Charlie Brown is frustrated at the crass commercialism of Christmas. Lucy recommends he direct their Christmas play to get over his doldrums, but he finds the play has become equally commercial. When he goes out to get a Christmas tree, he ignores Lucy's advice and gets a small, dull tree, and is laughed at and berated by the gang when he returns, by all except Linus. Charlie Brown's desperate plee to find the true meaning of Christmas ("Isn't there anyone who knows what Christmas is all about?") is answered by Linus, who takes the stage and quotes Luke 2:8-14. The gang no longer thinks the tree is worthy of ridicule. In despair because he thinks he ruined the tree, he finds the gang has fixed it and decorated it. As he is wondering what happened, they pause for a moment and yell "Merry Christmas, Charlie Brown" and serenade him with "Hark The Herald Angels Sing". A beatiful ending, compimented by the snow and letter design in the closing credits. There have been other Christmas cartoons with religious themes, but not enough.
This was the first full Peanuts cartoon, but they were featured a few years earlier in a series of Ford commercials.