Dinosaur Train has an excellent scientific backing with the most up to date information about dinosaurs. It also does a great job of teaching scientific literacy, both in general ("I have a hypothesis!" is Buddy's tagline, followed by Tiny explaining, "That's an idea you can test") and dinosaur-specific ("You have three toes, so you're a therapod like me"). All little kids should watch this show--it's a great counterbalance to the scientific illiteracy being promoted by certain institutions in the US today.
Not only is the science component incredibly strong, it also contains lots of great lessons on social and emotional skills as well as problem solving. (This is especially appreciated as I have [and was] a kid who tends to become obsessive about interests, and is lacking in social skills.) Social problems--like jealousy over a new friend being better than you at your best skill--are handled deftly, and every encounter with a new dinosaur ends with a new friendship being formed and a lesson being learned.
For example, Tiny Pteranodon is jealous when they meet Mikey Microraptor, who is even smaller than Tiny and has four wings where she has two. He can get into smaller places and retrieve things, which she has taken special pride in. She is jealous of him, despite his obvious admiration of her. Mrs. Pteranodon even explains to her that he's imitating everything she says because he thinks she's so awesome (partially because she can fly much better than he can--excellent science, of course.) But when the Dinosaur Train is stopped by a nut wedged in the exhaust pipe, Tiny and Mikey work together to get the nut out and save the day, and then sing a song about Tiny-and-Mikey Power. Everyone can learn from that situation, and it's not just a bland plotline like you'd expect from a kid's show.
Dinosaur Train is also interesting for parents. There's no objectionable content, but parents will recognize allusions like "Confuciusornis Says", and more dino-savvy parents will be amused at Arlene Archaeopteryx's German accent (the first Archaeopteryx was found in Germany). Also, nobody even knew half these dinosaurs when we were kids, so it's quite educational. Plus, feathered dinosaurs are awesome, especially Microraptor. Seriously, FOUR WINGS.