Breed doesn't always indicate suitability

My [Insert Breed] shouldn't do that!
My collie shouldn't be afraid of or mean to kids. My Doberman shouldn't be skittish. My Pyrenees shouldn't be trying to eat my chickens. My mastiff shouldn't be jumpy and nippy.
Maybe your breed shouldn't but YOUR DOG does.
Don't get me wrong, there is a lot you can know and prepare for based on breed. Breed tendencies are strong and purposefully bred into the DNA of these dogs, but every dog also has an individual personality and history that influence their basic instincts.
Early development and socialization as they grow is one of the biggest deciding factors for how a dog will behave. For example, you may own a breed that is traditionally very good with children. But if you purchased a puppy from a breeder who doesn't have children around and then raise your puppy in a child free environment you can't assume they'll even understand what a child IS the first time the meet them. Sometimes these dogs react fearfully or fear-aggressively on their first meeting with these "tiny aliens" and we don't understand why.
But if you think it through completely a young dog is constantly seeing things for the first time (something a lot of us don't understand anymore). They need time and space to feel comfortable with anything new in the environment.
The same theory applies to other breeds and their archetypes. A Pyrenees who has never seen livestock could be more likely to chase/attack. In theory if a young dog learned that it can chase the feral cats and hunt the rats in the yard, why wouldn't it make some sense that they could do the same to the chickens?
How do you fix it?
First of all pay attention to YOUR dog. If your dog doesn't fit their breed archetype, make note of it. Watch you dog and see what scares them and what they like. Keep an inventory and don't force them to be uncomfortable. You have to watch for early warning signs so that your dog doesn't feel the need to growl or bite to get away. Work with the dog you have, not the one you wanted.
There is a lot to how they are raised and what they learn about when they're young. If you are planning to introduce a new element to the environment, do so carefully and purposefully. Set your dog up for success. First time meeting kids? You can start with calm kids, or at a distance (go sit on the opposite side of a street at lunch time). Let your dog observe and if they choose to move forward you can reward that, if they move backwards let them. Your dog should only be near the kids if they are relaxed and happy. Keep interactions short and in control. Tell people to move if your dog starts to get upset (you are your dogs only voice). If all goes well do it again another time, if not take your dog back to the most recent step they were happy at.
Your dogs breed can tell you a lot, but your dog as an individual can tell you a lot more. Remember that they are individuals, meet them at their level, and strive to help them learn about their world in a safe and positive manner.