Super Mario series
Super Mario World
In Super Mario World, red, yellow, and blue Baby Yoshis are only found in Star World, where they hatch from eggs of the same color whenever Mario makes his approach. Feeding the Baby Yoshis five enemies will make them turn into adult Yoshi; however, if a baby Yoshi eats any power-up, it'll grow up instantly. Also, all the eggs Mario rescues from the Koopalings hatch into Baby Yoshis during the ending cutscene. Yoshi himself hatches directly into an adult when Mario uncovers his egg, but this is because Bowser trapped Yoshi in the egg.
Unlike their adult counterparts, Baby Yoshis appear to have beaks.
In the Game Boy Advance remake Super Mario World: Super Mario Advance 2, once a Baby Yoshi is found in Star World, it is possible to find their colorations in lieu of Green Yoshi inside any ? Block containing a Yoshi Egg. However, these Yoshis will not remain as babies. Instead, they will grow straight into adults like Green Yoshi. Mario's present form will determine what color Yoshi Egg will come out of the ? Block upon hitting it.
New Super Mario Bros. U
After a long absence, Baby Yoshis return in New Super Mario Bros. U. They now sound as they do in Super Mario World but high pitched. They are found in color swapped Yoshi Eggs. Like in Super Mario World, they can eat enemies, however they will not grow. There are three different colored Baby Yoshis: Bubble Baby Yoshis, which shoot bubbles used to defeat enemies and earn three coins; Glowing Baby Yoshis, which illuminate dark areas and stun enemies; and Balloon Baby Yoshis, which inflate like a balloon for vertical movement.
Baby Yoshis in this game run away like their adult counterpart if a player carries one while coming in contact with an enemy (if hit in the back). Like in Super Mario World, if the Baby Yoshi comes in contact with certain enemies, it will eat it.  Unlike their adult counterparts, Baby Yoshis (minus Glowing Baby Yoshis) follow the player into the End-of-Level Fortress. Baby Yoshis periodically appear on the World Map, and can be picked up and used in levels that normally do not have Baby Yoshis (minus Castle or Tower stages). Baby Yoshis can be kept until the player loses them; if there are multiple players, all players can continue to use Baby Yoshis as long as one player finishes the level with one. While swimming with Baby Yoshis, the player's swimming style resembles that of one who bears the Frog Suit or Penguin Suit, and the Baby Yoshi's normal abilities are replaced by an underwater spin maneuver that gives the player a speed boost. Baby Yoshis also vocalize to the music when picked up.
Baby Yoshis are also key factors in red Toad House minigames. In this minigame, they swallow icons that give the player a chance to win or lose the minigame. Balloon Baby Yoshis have the item icons which determine what power-up the player obtains, Bubble Baby Yoshis hold multiplier icons that determine how many power-ups the player obtains, and Glowing Baby Yoshis hold a Toad icon or a Bowser icon. The former allows the player to get the power-up, and the latter automatically marks a loss. The player must fit the Baby Yoshis in their respective color spots.
Super Mario World television series
Baby Yoshi is the young version of Yoshi in the Super Mario World television series episode "Mama Luigi". He differs from the Baby Yoshis of the Super Mario World game, Baby Yoshi is shown to be able to move on his own and use his tongue as a baby, was able to eat many enemies without growing, and did not possess any shoes on his feet either. He knows how to talk right from birth, but mistakes the first person he sees, Luigi, for his mother.
Baby Yoshis are known as Little Yoshis in Tetris Attack. A Yellow Little Yoshi appears in the game Tetris Attack. He appears to be Yoshi's friend although unlike other Yellow Yoshis he has the same colored shoes as Yoshi indicating some kind of close relation.
The Yoshis in Yoshi's Story were newborn, however they looked different from Super Mario World's Baby Yoshis. During the story sequences at the beginning and ending of the game, they were shown to have smaller and less developed bodies in contrast to the Yoshis seen only on the very first page in the intro. The Baby Yoshis in this game act unlike those of Super Mario World, as they have most of the abilities an adult would have, such as the Flutter Jump, Ground Pound, and the ability to stick out their tongue to eat Fruits and enemies. The Baby Yoshis also have the ability to lay eggs in Yoshi's Story, despite being newborn.
Yoshi's Island DS
A Green Baby Yoshi makes an appearance in Yoshi's Island DS. After the six original Star Children are introduced, a Baby Yoshi hatches, becoming the seventh Star Child. This Baby Yoshi is heavily implied to be the Yoshi, Mario's companion.
Super Mario RPG: Legend of the Seven Stars
Paper Mario series
A group of Yoshis children calling themselves the Fearsome 5 were encountered on Lavalava Island in Paper Mario. When they were first encountered, they were being watched over by Sushie, though they were thinking up plans of their own. When Mario later returned to the village after he discovers that the path to Mt. Lavalava is inaccessible, the older Yoshis are going berserk over the Yoshi children's sudden disappearances. Mario helped Sushie down from the tree that they trapped her in and found all five Baby Yoshis.
Paper Mario: The Thousand-Year Door
Yoshi from Paper Mario: The Thousand-Year Door is small like a Baby Yoshi, however other than being newborn he does not have the characteristics of the Baby Yoshis from Super Mario World as he is born with hair and is immediately able to talk after being born and even has pants. Yoshi is also able to move about in his egg.
Game & Watch Gallery series
Baby Yoshis have made frequent appearances in the Game & Watch Gallery series.
Game & Watch Gallery
Game & Watch Gallery 2
In Chef, Princess Peach has to feed a Yoshi, but if she feeds it overcooked food, it will revert into a Baby Yoshi. If she feeds a Yoshi enough cooked food though, it'll release an egg, which contains a Baby Yoshi.
Game & Watch Gallery 3
In Game & Watch Gallery 3 in Egg, if Yoshi eats enough cookies, he will lay an egg, which will eventually hatch into a Baby Yoshi. The Baby Yoshi assists Yoshi by temporarily eating cookies at a random angle.
A Baby Yoshi also appears during the credits, from an egg thrown by an adult Yoshi.
Game & Watch Gallery 4
In Game & Watch Gallery 4, the Baby Yoshi reprises its roles in Fire and Chef.
Appearances in Other Media
Six baby Yoshis are the main characters in volumes 19 and 20 of the CoroCoro Comics manga Super Mario-Kun, which cover the events of Yoshi's Story. They each have unique personalities and appearances, and accompany Mario and Poochy on a quest to retrieve the Super Happy Tree from the clutches of Baby Bowser. Throughout the story they are referred to as T.C.Y., or "Team Chibi Yoshi." Each of them has a page dedicated to their introduction with a four-panel comic that displays an outstanding aspect of their personality.