I know you have already bought presents, but maybe for next year... I buy my kids a canvas and oil or acrylic paints with some cheap brushes. I put them out on the grass on an old painting drop sheet and let them create an artwork. When they are done and the paint is dry, the artwork is hung in my study ('the Gallery'!). The kids LOVE doing the painting and I love the result! You could always hang the painting in their bedrooms if they wanted to. It entertains them for hours... I buy all the bits and pieces, including the canvas) from the $2 shops and it works out pretty cheap, maybe $30 for 2 x canvas, paints, brushes and a palette.

Just make sure you wait for a nice day and get them painting in an old pair of knickers because the paint won't wash out of clothing! (But a water soluble paint doesn't work as well).