Sharkboy: Usually, if you snooze, you lose. With Max, you snooze, you win.
Lavagirl: Row row row your banana split boat, gently down the steam of consciousness, merrily merrily merrily, life is Max's dream.
Mr. Electricidad: OK, kids, who's next? Remember, there are no dumb ideas.
Linus: Maybe we can freeze his circuits.
Mr. Electricidad: That's the dumbest idea I've ever heard. We're in the middle of Texas in August.
Lavagirl: Everything that is, or was, began with a dream.
Mr. Electricidad: What I can't believe is you dreamt me as a big round bad guy! I'm not bad.
Answer: Lava Girl is always hot to the touch. She can control when she throws magma, but the only way she can have any control over her actual body temperature is to control her emotions, which would naturally be difficult for someone her age. Even then, at her coolest possible temperature, her body temperature would still be very high. There are continuity issues with her body temperature throughout the film, ie, being able to sit on ice for extended periods of time without melting it, but the idea is she always has a very high body temperature.