This is the main feedback I have used to create artefact 6
I like it. I also agree with sam on the social media approach too.
Some possible developments I would suggest...
Add easy, medium and hard levels to each portrait/image
easy - image is transparent
medium - select parts of image is transparent, the rest blank
hard - blank background only
Maybe a larger iPad version would work better for kids too. Could be attached to the wall for passing kids to play on as art galleries are usually boring for kids.
Win medals rather than extra pens/brushes. Giving them more tools would be a natural development of the game anyway. Start with a pencil only then develop to full colour set of pens, etc. The rewards should be medals for completing each artwork. Gold for 1 - 10 seconds, silver for 11 - 20 seconds, bronze for 21 - 30 seconds finally 30+ seconds 'FAIL!' These times would obviously depend on how complex the artwork was to start with.
With using these medals you would still be able to include the leaderboard. 'John got a Gold medal for completing Fisher Boy in 4.5 seconds. Do you think you could beat his time?' Also you could after collecting x amount of gold medals give them 'youve won a £5 voucher to use at our gallery gift shop'
Overall I think its a brilliant idea that if produced well could spark more than just the 8 - 13 year olds playing on it. Yes, this means that I would be trying to beat Johns time of 4.5 seconds to gain myself enough starts to get a £5 voucher
f you wanted to take this further and put it out there as a proper artistic-kids product I would suggest running two Apps simultaneously, an iPhone App which forces kids to look at the images, but instead of draw what they see, they could answer questions about things like what colours were used, what type of paint, what was in the picture, how old do they think it is etc. And then you could have an iPad/tablet App, which could be downloadable, or just used within the gallery itself for kids to act out the original idea.