I work in a friendly restaurant as a part time barman to keep me going while im developing games. I have been working in this restaurant before i started the uni. thats about 7 years. (i know its sad T.T). But here is my observation from that 7 years. Hardly ever I seen a kid or a teenager coming with a laptop to a restaurant. Not even before the boom of touch devices. For the last 4 years though, I seen kids with their tablets and phones all the time. I am pretty sure you can experience this. Go to a friendly restaurant on a sunday afternoon and observe. I am confident you will come to the exact same conclusion.

any touch devices seems to me more user friendly and portable compare to a laptop. Which I believe is the reason why its so popular between kids and teens when they out of the house. Then again I am not sure entirely what they do in the house. that is something we can not observe to find out. Also Im sure computers are still major parts of student life in schools around the world.

Going for both computer and mobile device would seem advicable at first. until considering who you will be competing with.

if your going for a PC for an educational game, I think its hard to find a platform where you can exploit the market. Mainly because there are many educational pc games out there that is so easily accessible by anyone. typing "free flash games" in google will produce you a huge list. Can you compete with these providers? after all their money comes from advertising unlike you (presumably) relying on game sales.

Secondly, I seen you mentioning Steam. Steam has a system where a game project has to get a green light first before being published on steam. If there aren't any educational games in steam this is quite positively means that educational games didn't get a green light more likely because it s not a popular platform for educational games.

There is one place we can target for educational game though.The social game market. Making browser games with face book support would seem to me the best platform for an educational game. Then again this market is still booming with established companies. in terms of content you will be competing with them. Not to mention,games are free in social market. revenue is made by selling in-game items. Providing such services will come with a cost of running your own server(s) or a purchasing cloud space(s) somewhere. Which boils down to answering the following question " is my game worth the risk?"

based on these circumstances, I would suggest you to go for mobile devices if you want to start somewhere first. Then based on the success of the game you could decide to move on to the browser games. However if you have a great idea then going for browser game is equally advisable to going mobile.

Side note: you can make social games in mobile devices as well since the facebook SDK has massive support for both android and iOS.

Take a look at swrve and flurry's data reports, as that would help out. There is something else that was missing in the replies, and that is segmenting your market based on income.

iOS usually goes along with the middle & upper class, so if you want to make a serious game that's more geared towards in app purchases (for an educational benefit of course), I would stick with iOS. If you want to hit the schools though, as Sloper mentioned, then you would be generally looking as a one off purchase (if it is for sale) and go with PC.

Other things with iOS, other than the income class that tags along with it, is the demographics and stuff. You can find out more information there with swrve and flurry though. It's always good to do research with these things.

Cheers

Are you thinking for home use or education? I think phones are a bit small but kids love tablets and schools are definitely starting to use them.

For young children I'd say tablets are just more accessible, having watched all my friends have kids over the last few years they all like playing with iPads at age 2 and above but wouldn't be using a laptop/desktop for some years.