"Accept" button says I need to purchase app, but doesn't say how

Question

I purchased a new MacBook Pro in January. I setup accounts for myself (admin), son, and daughter (both Mac OS X users and Apple IDs). Yesterday I noticed from my Apple ID that the App Store said iMovie and iPhoto needed to be updated. I tried updating them, but it said they were purchased from another Apple ID, and I had to upgrade using that Apple ID. I logged into my son's Apple ID, ran App Store, and sure enough he had "Installed" them 4 weeks ago, along with GarageBand. I'm guessing this install was actually an upgrade since they came pre-installed on the machine. However, I'm not sure how this happened. He's downloaded other games, but doesn't recall ever updating anything.
In any case at this point what I want to do is disassociate these apps from my son's Apple ID so I can control their upgrade from my Apple ID. I tried deleting them from the LaunchPad. However, for GarageBand this left it in a state where I need to purchase it for $14.99. For iMovie and iPhoto, when I search for them for purchase, they are displayed with an "Accept" button rather than an "Install" button. When I click on "Accept" I get the following message:
"These apps cannot be accepted by your Apple ID.
These apps were already assigned to another Apple ID, and they will be available in that Apple ID's Purchases list. If you don't have access to that Apple ID and want to receive future updates, you will need to purchase the applications."
Problem is I can't find any way to purchase them from my Apple ID. How do I change the "Accept" button to a "Purchase" button?
BTW, I also tried deleting the apps and restoring from an old Time Zone backup, but still had the same problem. There's some database on the machine that associates these apps with my sons AppleID even though originally the came pre-installed.

Answer 1

Thanks for the info. Seems kind of messed up though. Why would Apple let any random user of a machine control all future upgrades of critical apps. I guess perhaps my admin password was needed at some point, which my son has. Still, seems this is something you should be able to undo.
I'm starting to get a clearer pictures of what's going on. These 3 apps are part of iLife 11 and normally cost $14.95 each. They come pre-installed on new machines, but it looks like at some point you need to associate this "purchase" with an Apple ID, and can only associate it with one Apple ID. Thus they are now irrevocably associated with my son's Apple ID.
However, if I wanted to shell out the money, it seems I should be able to tell this particular mac to forget everthing it knows about the purchase of these apps, and re-purchase them from another Apple ID. Although I doubt I'd do that at this point, if I by a 2nd Mac and properly associated these apps with my Apple ID on this 2nd mac, I should then be able to use this "purchase" to download the apps to the first mac I'm having a problem with. However, currently I can't even see a way to do this. Is there some App Store cache I can trash so App Store no longer knows which apps were installed by which Apple ID?