I found a very good website full of interesting activities for children. I especially advise the painting activities where you can explore all the great masters of painting.
In my Watercolor Adventure, I and my daughter played again with watercolor and it was so much fun . I think your children will enjoy this tutorial which you can find on Art Projects for Kids: Winter Birch Trees.
What you need:
Blue watercolor paint, paint brush, white acrylic color, course salt, watercolor paper, masking tape, scissors, water
How to do it:
First you need to attach the masking tape on your watercolor paper trying to make a shape of the trunk tree and with your paint brush watering all your watercolor paper.
Paint all your paper with dark blue watercolor paint, sprinkle some course salt on your paper and let dry.
Take off your masking tape and the salt, as you can see from the picture the salt adds some texture on the watercolor paper.
Finally you have to make some little dots with your acrylic white color and with blue watery watercolor
paint some lines on the trunk as you can see on the picture above.
But remember this idea came from this lovely website Art Projects for Kids: Winter Birch Trees.
Have fun !!!!