Welcome to the board. If they have no infections, and no injuries, there is no reason to give antibiotics, because that will create drug resistant bacteria that you won't be able to kill when they really get sick. Best leave them to build immunities and be strong as adults.
You say they are picking? Is there enough heat and space? Describe temps and set up of brooder from top to bottom and age of birds and we can give you an idea of what might be going on.
For the first few weeks, when they are sleeping, they can look pretty dead all stretched out and face in food and so on.