**Edit:**

Are the fathers
>! Machines

And their children
>! Products the machine makes. 

Reason:

Some of us with many
Some of us with one
>! Referring to the product each machine makes, it could make one or many. 

Out children vary in appearance even more than we
>! Different machines make different products that look different from each other. 

But helpers we are to one and plenty
>! All these products are used by people and they help us. 

A few of us knew our calling
>! The machine knows what is it supposed to do. I knows what particular "occupation" it is trained for. 

A few others knew our vision
>! Vision here might no refer to "sight". Instead vision could mean what they (machines) intend to do. 

Yet a few more knew our path (This one quite loosely fitting into the explanation)
>! If the machine is supposed to follow a certain path, it knows it's path.

Yet all fathers gave birth to their children
>! All machines made products.

Hint 1
>! There have been countless machines throughout the ages. 

Hint 2
>! The machines are "alive" (working/moving) while the products might no certainly be. 

Hint 3
>! The products do not die. They can surely be destroyed.

Hint 4
>! The children can be made of any material. The possibilities are endless. 


Original answer (confirmed wrong)

>! I believe the fathers are the thoughts that give birth to more thoughts (the children).     
>! Some people may have one thought. Others might have many.     
>! Thoughts vary widely from person to person.     
>! They help in situations too.     
>! You can call on a thought. You could also have a visual thought.     
>! As said before, thoughts give birth to more thoughts.