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.
