Meet the water nymphs (Hydriades or Ephydriades)

So I'm trying to write my own fantasy story with Greek mythology with nymphs, centaurs and other, but also own made creatures and stuff The story actually goes about a war between an old kingdom (ruled by humans of course) and the dark creatures (like mermaids, demons,...) The king and his queen were murdered in the battle and the dark creatures won. But before the battle had started the king and queen went to a lake where the Lamnades or Limnatides live.
They are a race of water nympfs that live by lakes. Gods used to give their children to them for a good education so when the king and queen desperately looked for a nymph and finally found one, they started begging to look after their child untill they were back from the war. Nymphs are good creatures and they knew what was going on between the good people and  the bad people in this world.
The nymph saw in the eyes of this little child that his parents knew they wouln't make it and accepted the offer.She took the little prince in her arms and swam away.
Under water she kept him in a bubble filt with air in a cave. For days she heard a lot of noise above the water level. Speers and swords were falling in the water, demons en harpies were flying above them and sometimes the water was red of blood.
A few weeks later The nymph didn't hear any noise above her for days... so she went looking what was going on. When she rose her head out of the water, she saw eveywere dead bodies of humans and dark creatures. The war was over so the nympf waited untill the parents came back, which they never did.
When she heared from the other nymphs that the dark creatures defeated all the humans, she realized that his parents, the king and queen who ruled the kingdom, where dead too. The nymph couldn't throw the child away like it was just a thing! So she decided to keep him and rase him as her own.