i unsuccessfully tried to get birds out between walls and now baby birds can be heard. I know I must wait until they leave nest to patch wall, but what about possible health risk from bird droppings inside wall?

After the young birds have left the nest, wear disposable gloves and remove the nest ,if you can access it. It can be disposed of in the trash (seal the bag and store outside in a garbage bin until pick-up day). If you can access the site with a shop-vac, try getting out any remaining droppings. Wearing a disposable mask won't hurt, but isn't really necessary as long as you are in a well-ventilated space. Health risks should be minimal. Problems occur when there are lots of nests/droppings and the area isn't well ventilated. Doesn't sound like that's what you're dealing with there.