It's true that Sarina and that Doc reincarnated as Ruby and Aqua... and being able to hold a high level discussion at 2 or 3 years of age is already un natural.
But somehow they've kept the supernatural limited to just that, some arm twisting for the pitch and keep a shorter timeframe for the story.
They could totally use that card again, but it doesn't feel like they will. That would be a shame if they did because almost every character with some developpement already feels OP.