Basic how to:
Spread out newspaper or something to cover your table. This could get messy!
Lay out your coffee filter and offer paint to your child. This can be done with either acrylic or watercolor paint. You will get different results with each kind of paint. Acrylic will stay put but the water color will spread in all different directions.
If you have food coloring you might offer that to your child as well. It would be fun to set out a couple of different options for coloring You might even offer crayons and markers as well.
Once your filter has accepted all the color it's easy to make the butterfly body. Fold your pipecleaner in half. Twist the bottom inch near the fold into a tail. Crunch your filter in the middle and put it on top of the tail. Twist the top of the pipecleaner around the body and use the top of the remaining stem to make your antenna's.
These look beautiful hanging in the window.
To extend the activity you might read a few books about butterflies. Here are a few I found:
From Caterpillar to Butterfly by Deborah Heiligman
Where Butterflies Grow by Joanne Ryder
La Mariposa by Francisco Jimenez, illustrated by Simon Silva