The PBS masterpiece series "Agatha Christie's Poirot" is indeed a very good one for a child to watch:
- The episodes are elegant theatric plays in the British movie tradition.
- Each one is a complicated detective story challenging a child's understanding.
- Although the content is about solving crimes, the scenes are usually not too scary or violent.
- Actor David Suchet portraits the character with great style.
- There is always a sense of humor. (In the episode "The Disappearance of Mr. Davenheim", Poirot studies how to play some magic.)
- There is always a sense of humor. (In the episode "The Disappearance of Mr. Davenheim", Poirot studies how to play some magic.)
- It is on PBS, so no time wasting advertisements during the show.
The whole series is listed here on wikipedia or imdb. You may read about some episodes on Poirot Investigates as well.