From the Super Mario Wiki
Little Mousers, also known as Squeeks or Squeaks, are a species of small, mice-like creatures who wear bandannas that obscure their faces. Judging from their English name, one would think that Little Mousers are relatives of Mouser of Super Mario Bros. 2. However, their Japanese name, チューさん chuu-san, defies that notion, which is why they have been renamed in later games.
Super Mario World 2: Yoshi's Island / Yoshi's Island: Super Mario Advance 3
The first appearance of Little Mousers was in Super Mario World 2: Yoshi's Island, were they appeared infrequently as enemy creatures who would try to steal a Yoshi's egg and scurry away with it, into their burrows. Little Skull Mousers also appear - they are just like normal Mousers, except they wear skulls on their heads and cannot steal eggs.
Mario Kart: Super Circuit
Paper Mario: The Thousand-Year Door
In Paper Mario: The Thousand-Year Door, Little Mousers were renamed Squeeks and were shown to be one of the primary inhabitants of Rogueport and Rogueport Sewers; a white Squeek, known as Ms. Mowz also appears in Paper Mario: The Thousand-Year Door as an optional partner of Mario.
Mario Party series
Mario Party Advance
In Mario Party Advance, a Little Mouser named Mouser appears as the boss and owner of the Duel Tower. He challenges the player to the game Chicken!. If the player wins, he receives the minigame. The ending said that he was bummed that Whomp left the Duel Tower.
Mario Party 8
In Mario Party 8, a sub-species of Little Mouser, called the Mowz, also makes cameo appearances in the boards Shy Guy's Perplex Express and King Boo's Haunted Hideaway. Also, a Mowz can be seen in the Star Carnival at the menu screen, along with famous enemies such as Koopas, Chain Chomps and Shy Guys.
Yoshi's New Island
Little Mousers are set to appear in Yoshi's New Island.
Names in other languages