It's good to know that nearly 100 years on from the films, Chaplin's comedy hasn't dimmed. In fact, in some ways I find his pantomime mastery and gentle pratfalls and cheer even more soothing, in a 24-hour-news, text-a-minute kind of world. I dig having a kid who appreciates Chaplin, at least for now.
If I had to pick a favorite Chaplin film, I think I'd go with 1936's "Modern Times," which came towards the end of Chaplin's peak fame. It was the sound era, although Chaplin remained a dogged fan of silent film and pantomime, and sound effects were used throughout "Modern Times." "Times" critiques the pitfalls of capitalism, machines and mass-production, but doesn't preach as much as Chaplin's later films tended to. In the middle of the Great Depression, the Little Tramp's hardship and poverty seemed more relevant than ever.
I also love Paulette Goddard's fiercely feral performance as the "Gamine", a barefoot, homeless young lass Chaplin befriends. "Modern Times" sums up the slapstick, hopelessly romantic and cynically observant parts of Chaplin very well. Chaplin's idealism is a huge part of his charm (and a part of why as he aged, and faced McCarthyism and other problems, his films became far darker and less popular).
And is there any movie-ending musical number more blissfully silly than the "nonsense song," in which, for the first time, Chaplin's Tramp speaks? (Um, kind of.) If you've never seen it, here you go -- all you need to know is that as the Tramp prepares his big musical number at the restaurant, he's lost the song lyrics he'd hidden in his sleeve. Time to wing it! A more cheerful celebration of nonsense I've never seen. With subtitles for the "lyrics"!