The first season of Rugrats was much different compared to the rest of the series.
- While the "classic" episodes that most people think back on were about the friendship of the whole gang, who are all well-developed characters, working together to deal with various issues, fears, superstitions, things the adults are doing, etc, the first season is a way starker show, in which many episodes follow a similar formula: Tommy (and sometimes one or more of the other kids) is brought by the adults to a new place (the movies, a restaurant, a baseball game, etc.), wanders away without the adults noticing, gets into all kinds of trouble and causes slapstick chaos. In some of these episodes, Tommy never even speaks and just acts like a real baby. But eventually, this formula was phased out and the writing became much more character-driven.
- The art style was also quite a bit cruder in the first season, and Tommy spoke with more of a grunt.
- The pilot episode, "Tommy Pickles and the Great White Thing", was even stranger, with more bizarre animation that looks like Don Bluth on LSD, adult characters having long necks, Tommy's Grandpa being called Stu Pickles, Sr. rather than Lou, and a different voice actress for Tommy (Tami Halbrook, who would later show up in a couple of episodes).
- During the first season (and in S2's "Chuckie vs. The Potty"), Chuckie is said to have a living mother and she actually briefly appears in one episode (with a completely different design). He isn't revealed to be a single parent child until Chas becomes a more prominent character midway through season 2, and it's later stated that she died prior to the series.
- Chuckie was also a bit more of a Jerkass in the first season, often angrily complaining and yelling at everybody when things didn't go his way. He wouldn't become the disagreeable yet lovable sidekick we all know and love until the second season.
- Funnily, it also seems like the characters experienced a little developmental regression after the first season. In season 1, they're able to successfully count to three and articulate fairly sophisticated words (even if they mispronounce them). Neither of which they would be able to do again from S2 onwards.
- In the first season, it was implied Tommy could speak a little, as there was the occasional episode where he didn't speak as he normally did and was mainly around adults at the time. The second movie establishes Chuckie as the first baby to speak.
- A few early episodes seem to suggest that Reptar is a cartoon character in the Rugrats universe, and that he's capable of speaking. "Reptar on Ice" features a costumed actor singing his lines in a Reptar musical, "Toy Palace" features an animatronic Reptar toy that repeatedly bellows "Halt! I am Reptar!" when Tommy presses a button, and "Reptar's Revenge" features another costumed Reptar actor who openly talks to children while in costume. Later episodes, however, would more clearly establish Reptar as a parody of Godzilla who can do nothing more than roar, and primarily stars in live-action movies imported from Japan.
- In the first few episodes Tommy wore a red shirt instead of a blue one and sometimes wore overalls.
- In the first season, Angelica was more of a standard bully character and it was the second season onward that characterized her as the chronic liar and manipulator and Jerk with a Heart of Gold that she would become more well-known for. She also wore this strange white thing that appeared to be a diaper or a pair of undies over her tights in season one.
- In "Chuckie Loses His Glasses," the babies all refer to Chuckie's glasses as his "extra eyes." In later episodes, including one flashback episode that shows their first meeting, they know the word "glasses."
