These are the list of current (and up-coming) child villagers, which are either insects, fish or sea creatures.
Not all images can be found, though.
Arnold[]

Arnold.
Arnold is a red anchovy with blue and white stripes who lives in river mouths. He is a "child villager" because he is a small fish. His personality is Jock and his birthday is on 4th of July and he is a Gemeni. His catchphrase is "plankton".
Zephyr[]
Zephyr is a goliath beetle, making it a child villager because most insects are small. His personality is Snooty and often lives in Ern's house (note that Ern is a statue which can be revived). His catchphrase is "buzzer".
Eagle[]
Eagle is a dung beetle which is coloured like Inkwell, a Splatoon-themed villager. Their personality is Normal and lives in Viche's house. (Note that Viche can be obtained with a splatoon Callie amiibo or if your lucky at the campsite.) They do not have a catchphrase.