Please see the following link to some activities that the Tate have put online that you might find useful: 

Tate Kids

Below are some artist work cards for Gold class - they're all abstract painters and there are some links to their work at the Tate gallery.  Most of the students have painted a great abstract painting so hopefully, they might remember some of these artists!

You have two tasks, one to draw directly from the artist painting and the next is mixed media - using pen and pencil together if those they can draw their own abstract drawing.

Patrick Heron

Peter Lanyon

Clyfford Still