Everything I've found on-line says they'll definitely eat the eggs, but will
they eat the baby fish once they've hatched?

There are a bunch of things that eat babies....but most of the time the babies
will come out on top.....I have on average 3 koi and 20 or so goldfish that
make it to the following summer. The largest preditor in my ponds for babies
are frogs. Herons come in every so often and take the adult fish. Jerri

http://www.fringeweb.com/Ponds/JerrisPond