One word of caution on this one - the subject is a forest fire that threatens to burn down the entire village of Pontypandy. Although suspenseful, it got my kid a little alarmed at first. He got over it, but be cautious if you have a younger kid or one who is sensitive to scary situations on TV.
My three-year-old son is hooked on Fireman Sam, which we are streaming for free with Prime. The movies are great because the series episodes are only 11 minutes long, meaning I have to start them up over and over again. The content of the series is great, always appropriate and with a good, positive, safety-related message for the kids.