There were particularly odd rules regarding children buying alcohol. In the 1920's it was still common practice for parents to send their children to the pub to fetch beer. I know this through my Mum, who regularly fetched beer for her mother. It was fine for underage kids to fetch beer, as long as the container was sealed.
My Mum fetched a jug of beer, which doesn't sound very sealed. But it was, because the pub would fit a paper seal over the top so it could be seen if the child had taken anythiong from the jug. Amongst the teetotal nutcase brigade wther was a great deal of concern about "sipping" - kids having a try of their parents beer on the way home.
William Thomas Prior, the Grosvenor Hotel, Maldon Colchester, was summoned at the local Police Court Tuesday on two charges of supplying intoxicating liquor to two children under 14 years other than in a corked and sealed vessel. P.c. Clear said he stopped the children carrying unsealed bottles containing ale. He took them back to the premises, where defendant said, "I did not ask the children their ages. I thought the order was cancelled in September. The bottles had screw tops." — Defendant said he was under the impression that if a child was served with a closed vessel be was all right. He really thought the order had been scrapped. There had been a good deal of confusion resulting from D.O.R.A. —The Bench imposed fine of £1 in each case — £2 in all. "
Essex Newsman - Saturday 21 January 1922, page 1.
I can understand the landlords's confusion. There had been a host of wartime regulations, most of which were removed at the end of hostilities. But not all were. For example the hated afternoon closing period.
One thing confuses me. I thought screw-top bottles had a paper seal over the top, too. Ones like this:
Which makes me suspect that it wasn't bottled beer the kids had bought, but draught beer pulled into a bottles.