Kawa akago

Kawa akago (Japanese: 川赤子 or かわあかご, meaning "river baby") or kawa akaji are cousins of the kappa, and are a trickster yōkai who look like small, red-skinned babies in Japanese mythology.

Myths & Legends
Kawa akago appear on riverbanks and call out to passersby, perfectly mimicking the sound of crying human babies: “Waah! Waah!” (Japanese: “ Ogyaa! Ogyaa! ”) When someone wanders down to the river’s edge, the kawa akago retreats further into the underbrush and calls out again. This continues with the yōkai leading its victim further and further into the river. Finally, it sneaks up under the unsuspecting human, pulls his legs out from under him, and sends him tumbling into the river. While this is only meant as a prank, some people drown in this manner. This makes kawa akago a fairly dangerous yōkai.

Origin
Similar yōkai called yama akago (mountain baby) are found in Akita Prefecture (old Dewa Province). They hide in leaf piles in the mountains, and when people step on the leaves, they call out in a loud voice, “Ouch! That hurt!” Then they laugh and vanish into thin air.