Why are they just laying there?...

We've been noticing that the alevins have hatched and look great, but they lay around in the bottom of the net a lot.

That is because in nature, as soon as they hatch, they burrow down into the sand, soil and rocks in the bottom of the river.  This is so that they can stay hidden because it is very dangerous to be so small in nature.  Other fish, birds and even turtles and frogs act as predators to the tiny trout.  So by instinct they are laying low and hiding out for the first 2-3 weeks that they are alive.  As soon as their yolk sac is absorbed, they'll be swimming about and much more active.  Look at the pictures below and see if you can notice how some yolk sacs are already getting smaller than others.  By late next week, you won't see any at all!