Using old iPad for kids only

If you wish to stop email arriving on your old iPad, just delete the email accounts from the iPad; this will not impact your other devices:

Settings > Mail > Accounts > [Your email account] > Delete Account

You can prevent other services from synchronising documents and data via iCloud by disabling the services that you don’t want to synchronise from settings. Again, on your old iPad:

Settings > [Your Name / AppleID] > iCloud - turn OFF services that you don’t wish to synchronise via iCloud

You might even consider signing-out from iCloud entirely - or creating and using en entirely different AppleID account for your old iPad. If this is appealing, follow this process to completely wipe the iPad, after which you can set-up again “as new”:

What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support

You are very welcome. Don’t hesitate to return to this thread if you need any additional guidance.