Is it possible to make 'admin' user apps available on other user accounts? With 4.2 on my Nexus 7 I have a few separate user profiles.

I have a number of kids games installed on my tablet admin account ('Rob'), with that account attached to a Play account.

I'd like to make those games available on another non-admin ('Callum') account, which is not attached to a Play account.

How can I do this?
As far as I know: Not at all.

Each user account is strictly separated from another and there is no shared folder or app sharing concept at the moment.

I haven't checked your specific question in detail, however each user has their strictly separated userdata partition where everything is stored (even their media, on Nexus devices) and cannot access any other's data residing in their userdata section, which includes user installed apps (they're in /data/app/).