As for the hawk feathers, don't touch! (legally) My thought on the kiddos collecting them is this: let 'em. What does it really hurt? I might have seen a bluejay feather or two get picked up in my day...
Regarding the flamingo feathers, if the keeper let you have them, and they aren't wild birds, why wouldn't they be okay? It's a captive bird's feathers. Just like using, say, macaw feathers.
