Damn, showing my age :lol:
Trying to redeem myself now:
Looking at the sort of sites that come up near the top of Google, it seems this dressing up lark is squarely aimed at young girls. The online stuff is simple drag and drop item of clothing etc. the kind of game you happily let your 8 year old girl play on the internet because its easy for them, and it keeps them busy for a while.
Sure some searches will be parents looking for sites to let their kids play on and even some parents looking for games to buy, such as the current batch of Wii or DS games of this genre...but mostly i'm just seeing online flash games as the main reason for searching for this phrase.
With all this in mind, I don't think a store will be successful as kids this young don't have online purchasing power. Even if you storebust a load of Wii and DS games about dressing up, after a kid has dragged their parents to the PC saying 'i want this', i think a parent is more likely to buy them from a reputable games company.
I think your best bet is to have a site rating loads of these flash dressing up games with links to the games online. Go on about be safe for kids and child friendly games. (suits the extension as well) Then have a load of Adsense adverts and just let young kids jab at any old adsense link as they're surfing the site.