People are saying that General Yunnan is their mother but she's a Newt while Polly and Spring are frogs just like Hop Pop! There are no newt and frog hybrids, but If General was their mother then wouldn't Spring have a tail and Polly would be a lot longer?
My Theory is that they are adopted. Their parents could've gotten killed by the toads because it explains Polly's personality. She is very feisty and likes to fight a lot so probably their parents were soldiers and probably got killed by the toads. Hop Pop adopted them and raised them. JUST A THEORY! You don't have to agree. :)