The Tadpoles are an optional character encounter. You find them after solving the puzzle that fills the underground river with water. You are not required to talk to them and can safely ignore them without having much impact on the main story.
The Tadpoles give responses to the player upon their first, second, and third time talking to them:
1. "My dad is dead."
2. "My dad was eaten by a snake."
3. "You killed him." - After this response, the tadpoles will cause tiles you are standing on to break apart, causing Viola to fall into the water and meet her demise (supposedly in the form of drowning, although the Tadpoles could have had something to do with her death, beyond just breaking the tiles she was standing on).
After you wash the Red Shoes in the river in order to obtain the Glass Shoes, interacting with the tadpoles garners the message: "Dead Tadpoles floating in the water."