Togepi has never been officially considered a baby Pokémon. The only thing where they ever used the term was the TCG and it as well as Riolu and Toxel are just basic Pokémon there.
The main games have never used the term, but it is still a discernible category of some form based on Egg Groups. There’s a reason why Pichu, Cleffa, Igglybuff, Togepi, Tyrogue, Smoochum, Elekid, Magby, Azurill, Wynaut, Budew, Chingling, Bonsly, Mime Jr., Happiny, Munchlax, Riolu, Mantyke, and Toxel are all in the Undiscovered Egg Group. That’s not a coincidence.