I'd be very cautious about this - As feathers are developing the shafts are full of blood - in Falconry, we say birds aren't ready to fledge until they are 'hard penned' meaning, the feathers no longer have blood in them.
You can inadvertently injure your birds very easily -
I'd recommend putting them in a brooder with higher walls, or cover the top with mesh or hardware cloth to keep them from popping out. As for flying - I dunno, I have never had a problem with my birds - they only fly up to their roosts at night.