Have a look at colourme_hp for lots of line art just waiting to be coloured in. There's some very sweet pictures in among all the NC-17 stuff!
Either colour it digitally or print it out, use whatever traditional media you prefer and then scan the completed image back in. Fun for all the family!!
Here's my attempt:
And here are some of my favourite line arts for you to pick from:
Bill/Fleur: Walking and kissing. Here's your chance to have a go at some scars. LOL
Sirius and baby Harry
The founding four