The offense is 'trading without a license'.
Licenses cover a veriety of things, but in the case of booze and porn it's 'Sale by retail'.
Now you don't actually have to charge for it to need the license. The Porn was a 'free gift' received on the condition you spent £5. As far as the law is concerned, the porn was not free. It's counted as part of the transaction (on the fairly fair assumption that you are recovering the cost through profit from the other goods).
So they need a Sex license for the porn (if it's R18), and two alcohol licenses (premises and personal) or a Temporary Event Notice for the booze.
The food and drink also requires a late night entertainment license.
As far as whether it was given to children, this gets a little more complicated;
The License exists as a means of trying to ensure the underage don't obtain the item.
By failing to have a license, there's a presumption that you are not too scrupulous
You get shafted
It's true that it'd be hard to prove they gave it to children, but they probably wont even bother to try (either that, or one of their 'test' purchasers was a minor)
When it comes to Licensing, the Police/Local Authority will take every step they can to try and catch you out. If they manage you get a fine of £80 minimum, and could do 6 months hard time (for alcohol, not sure of the punishments for sex)
Anon, cos I wouldn't want to lose MY license!