Generation 1. (Please note that this is my opinion on what Pokemon look like babies. They might not be classified as baby Pokemon)
Poliwag- it's based off of a tadpole, a baby frog. Location: Brooklet Hill, Malie Garden
Generation 2.
Pichu- Route 1, Hau'oli City
Cleffa- Mount Hokulani
Igglybuff- Route 4, Route 6
Togepi- Trade/Migrate from another game
Teddiursa- it's a baby bear. Trade/migrate from another game
Elekid- Route 12, Blush Mountain
Magby- Wela Volcano Park
Smoochum- trade/migrate from another game
Larvitar- it's based off of a larva, a baby beetle. Trade/migrate from another game
Generation 3.
Seedot- it's based off of a seed, a baby tree. Trade/migrate from another game
Ralts- Trade/migrate from another game
Whismur- look at it. It's totally a baby Pokemon. Trade/migrate from another game
Azurill- Trade/migrate from another game
Skitty- it's a baby cat. Trade/migrate from another game
Wynaut- Trade/migrate from another game
Generation 4.
Budew- Trade/migrate from another game
Buneary- Trade/migrate from another game
Mime Jr.- Trade/migrate from another game
Happiny- Route 1, Route 4, Route 6, Hau'oli City, Lush Jungle
Bonsly- Route 1, Lush Jungle
Munchlax- Route 1
Riolu- Poni Grove
Mantyke- trade/migrate from another game
Generation 5.
Lillipup- It's a baby dog. Route 4, Route 5, Route 6, Brooklet Hill, Paniola Ranch
Blitzle- baby horse/zebra. Trade/migrate from another game.
Tympole- It's also a tadpole. Trade/migrate from another game
Sewaddle- do I have to explain any more than I already did? I'm tired of explaining. Trade/migrate from another game
Petilil- Melemele Meadow, Ula'ula Meadow, Malie Garden, Poni Plains, Poni Meadow
Scraggy- trade/migrate from another game
Gothita- trade/migrate from another game
Ducklett- trade/migrate from another game
Deerling- trade/migrate from another game
Cubchoo- trade/migrate from another game
Rufflet- Sun: Route 3, Moon: trade/migrate from another game
Vullaby- Sun: trade/migrate from another game, Moon: Route 3
Generation 6.
Litleo- trade/migrate from another game
Flabebe- (I don't know how to make e's like that) trade/migrate from another game
Skiddo- trade/migrate from another game
Espurr- trade/migrate from another game
Generation 7.
Rockruff- Ten Carat Hill
Fomantis- Route 5, Lush Jungle
Stufful- Route 8, Akala Outskirts
Bounsweet- Lush Jungle
I don't know if this is exactly what you were looking for, but I hope this helped! I spent an hour doing this.