IOS – put an app bought with an old ID on the iPad with its new ID

Yes, you can have apps installed from different Apple Id's. Simply log in with whatever account you both want to use for purchasing. You can log out and back in with a different App Store account at any time.

I have multiple accounts, and multiple devices sharing applications.

To follow up the other responses, your App Store account can be separate from your iCloud, Messages, and FaceTime accounts. I use a separate account (Apple ID) for iTunes purchases than my iCloud account.

Some people even split things the opposite way - sharing email, FaceTime and messages but having different store accounts. It's really up to whatever works best for you and your devices.

This all depends on where you want to go with the Apple IDs after this. Even if you want the kids to all have their own Apple IDs in the future, because it is just one device, it probably is a good idea to just stick with one Apple ID.

In this case, I would recommend using your Apple ID for purchasing content. This way, any time apps are purchased, they stay with your account, instead of having a third account to try to remember for buying apps and such - after the kids get their own devices and Apple IDs. Parental Restrictions on iOS devices have a nice amount of control over disabling features and other things such as setting age limits on purchasing content, or disabling the App and iTunes stores altogether.

To remove your personal information:

1. Open Settings.app and scroll and tap on Mail, Contacts, Calendars.
2. Delete any of your mail accounts (if applicable) that you don't want your kids to access including the first one - "iCloud".
   1. When you do get to iCloud, scroll down to the bottom on that one and tap delete. Don't worry, it's only removing the account and information from your device - not the account itself.
3. Go back to the main Settings.app menu and scroll down to Messages. Scroll to "Send & Receive at". Tap the Apple ID at the top and Sign Out".
4. Go to "Facetime" and make sure you are signed out of your Apple ID.
5. To make sure your old iPod doesn't download any new content that you download onto your new iPod, go to Settings.app > iTunes & App Stores and disable "Automatic Downloads".
   1. After this go to Parental Restrictions and see if there is an option to disable changing that Automatic Download setting (I'm not sure on that one).
   2. The for sure method, in addition to disabling Automatic Downloads is to disable iBooks, iTunes, and App store. The device will not download content when these stores are disabled.

Now, after that you could set up an Apple ID for Facetime, Messages, and iCloud, if you wanted. You would then use that to just log in those places and not the app store.