I read somewhere bread is not good for them. Cant remember why though.
You are correct! It is not a very balanced food for a full diet. However if the birds are needing to fend for themselves a mother hen would announce this as a food source. It is more nutritionally dense then some things. Bread will not hurt them, chickens are really amazing eaters. You probably should avoid feeding bread to ducks. Ducks must drink lots of water with their grains and sometimes a bunch dry bread can cause problems. Limited bread in the water will not kill a duck.. the can eat some grain.
In all honesty my rather spoiled hens will reject bread treats as they prefer fruits and veggies, do remember that they are also able to eat as much pellet as they want. So bread isn't really that exciting to them.
I have sometimes seen hens lift a piece of food and drop it in front of the chick... I´m assuming this is the same thing? 
what foods are good for the chicks? They are so tiny!
When I go to the park, I usually take bread, my leftover seeds mixed with new seeds, and a couple of buckets of chopped veg (peppers, cabbage, carrots, cauliflower etc)
In the park there are lots of animals, I like to do a full lap of the park and feed as many as possible, I always make sure I give food to the chicks, and I try to avoid the pigeons (they can leave and scavenge from local cafes).
Is there any other foods I can give them? Things I can feed to ducks, chickens, swans, quaker parrots and peacocks.
Awe yes! That behaviour of the hen lifting it and dropping it. That is how they help teach their babies.
This is a beautiful video of a hen and her chicks. She really wants her babies to eat birdie bread. Chicks need a much higher calories diet than adults. The crumbs you see are a commerical chick pellet. They call it grow pellet.
These are some good street snack ideas for Ducks and Chicken. I do not have experience with peafowl.
Ducks:: Peas, meal worms, snails, if you like/eat prawns you can feed the legs and heads (clearly be smart about this with freshness etc), most veggies scraps are great too -NO ONION. If feeding grains feed near the open water so that the ducks can drink as needed.
Chickens:: rolled oats, barley, scraps meat pieces if you cook that sort of thing, watermelon, grapes or sultanas/raisins, any orange veggie:: pumpkin, sweet potato, carrot, etc. You do not need to cook sweet potato for them. They even eat sweet potato leaves. *Reminder that a sweet potato is a tropical root vegetable, it isn't a night shade plant.
Helping Mummy hen out:: crickets, you could try buying a small bag of starter feed (19%-20% protein)
Both ducks and chickens are omnivores. The best treats are things that are hard for them to find in the wild. High Vitamin A and animal protein sources will be harder to find. They have very strong gizzards. Chickens eat rocks, dirt and such to help them. They will eat sunflower seeds whole for example, this is normal for them
