My little sister found 2 baby birds, dont know what kind, just out of the shell.?

My little sister found 2 baby birds, dont know what kind, just out of the shell and we cant find the nest. They are almost hairless, cannot open their eyes and dont "chirp/cheep". They will open their mouths for food (she is mixing warm milk with egg whites/berries or worm). She has kept them inside overnight and we just tried making a little nest to put them in a tree to see if momma bird will come find them. But if they are still there in an hour, we dont know what to do.... there is no wildlife rescue around. Help please!?!