Was there another monster in the water?
At the beginning of the film, the comic relief guy sees a pair of glowing white eyes in the water. This creature disappears.
Later the two Gappa monsters emerge from the volcano. It appears they were at rest and were not disturbed until their child was taken from them. But their eyes appear to glow red and not white.
Maybe I missed something, but the impression I got was that the creature was at rest in the volcano until it was disturbed. Was the creature at the beginning another monster?