For the past 13+ years of homeschooling my children, we have been slowing trying to incorporate more and more brush drawing and sketching.
Sketching is done with pencil. It allows for shading with one color OR with the modern invention of inexpensive colored pencils with many colors! It is one of many ways children narrate in this house.
Brush drawing is done with a brush and one or many colors. Usually we find watercolors to be the easiest way to have many colors. If wanting to only use one color, a brush can also provide some depth of colors. Both with layering more and more paint, or by diluting the color you've picked.
SO how do you begin with Brush drawing?
In the beginning, I don't offer my children expensive paints. When they are learning to hold a brush and getting more confident, I use the lesser quality brushes. I don't buy the $.99 kind, but I don't spend hundreds of dollars. Somewhere in the middle in which the paint is quality and the brushes have to be taught how to be used.
If a child has only been working with crayons and pencils up to this point, the pressure they offer to a brush can easily ruin the tip. It requires some basic first instructions and much follow up as they learn. Much time must be spent helping them to have a light hand with a brush. Encourage acknowledgement of the tip of the brush.
We have practiced touching the top of our hands with our paint brush. This allows them to feel what the paper might feel. It's a very gently stroke. Try it. Take a simple paint brush and use it to brush with no water or paint on the top of your hand. See if you can keep only the tip of the brush having contact with your hand. Now try "dry painting" on your neighbors hand. See if they notice when you push to hard or too light!
We also have experimented with only water in the beginning. Rice paper allows a child to paint over and over with a wet brush until they see how gentle to be. This Japanese painting set has been a way to slow a child down and increase their attention span. The rice paper slowly dries to extinguish the painting.
Here's what we have learned. Good quality paints are great. If you are beginning a child on dry brush at age 6, perhaps you can begin with some acceptable paints. I like to use this one. Buy quality paper. But cut it into smaller squares/rectangles. Trying to brush draw a 8.5 x 11 page is overwhelming (even for this mother). A 2 inch x 3 inch is much easier to begin.
Here are some Parents Review Articles that might help you:
Vol 2, pg 337+
Vol 3, pg 348+
Vol 14, pg. 21+
Vol 14, pg 277+