To put this into context, according to The Pub and the People, there was almost no underage drinking pre-war.
"Girls in Public House
NO SHANDY, SO DRANK MILD
TWO 17-years-old girls, Dorothy Elizabeth White, milk bar attendant, 2, James Street, Rugby, and Sybil Georgina Humphreys, coil winder, 14, Maple Grove, Rugby, were summoned at Rugby on Wednesday, before Alderman C. W. Browning, M.B.E. (in the chair), and Mrs. E. D. Miller, O.B.E., for purchasing liquor for consumption on licensed premises whilst being under age 18.
Both pleaded guilty.
P.S. Sutton said he went to the public bar of the Saracen's Head, and saw the two defendants, together with another girl, at a table near the door. Each girl had a partly-filled half-pint glass of mild beer in front of her. He questioned defendants, who said their were between 17 and 18. He told them they were committing an offence and asked for an explanation, and Humphreys said "I thought it would all right have a shandy, but after I had had drink Dorothy said it was beer and not shandy." White said she thought it would be all right to have a shandy, and she bought the drinks, but there was no lemonade so they had beer. Witness ascertained that the drinks were served by the wife of the licensee, who thought the girls were over 18. He also ascertained that each girl paid for her own drink, and White took the money to the counter.
Superintendent Wood said nothing was known against either of the girls.
The mother of Humphreys said she would like a little supervision for her daughter, who was easily led. The girl’s morals were all right, but she thought she could come on at what hour she chose at night.
DIDN’T KNOW DIFFERENCE
Another girl, aged 15 3/4 years, pleaded guilty to a similar offence at the same time and place and was placed on probation for 6 months, and ordered to pay the costs of 4/-.
P.C. Sutton said the girl said in explanation "I understood it would be all right yo go in and have a shandy. I don't know the difference between shandy and beer."
Superintendent Wood said nothing was known against the girl, but the police regarded these offences as serious.
The girl told the Bench she was sorry. It was about the second occasion on which she had been in a public house.
The girl's father said he was astonished to hear about the case. His daughter had not been brought up that way, and he did think her brothers and sisters in the Forces either smoked or drank.
The Chairman said the Bench took a rather serious view of the case.
Rugby Advertiser - Friday 28 January 1944, page 5.
The older girls were just a few months under age, but were put on probation. For drinking a half of Mild. It seems way over the top. Would it have been considered so serious had they been boys? I think not.
The statement "nothing was known against either of the girls" is revealing and is why I think the police found it a serious matter. The underlying concern appears to me that the girls were prostitutes.
It's interesting that the licensee wasn't prosecuted. That's what would happen today and the girls would be just told off.
On top of it all, a WW II Mild could well have been under 3% ABV. Hardly any stronger than shandy. A half was wasn't going to get you anything like pissed.