Times change…during my formative boozing years in the ’70s children were virtually absent from pubs, perhaps allowed in beer gardens at the landlord’s discretion with the strict stipulation of them being ‘seen but not heard’ i.e. sit at the table and be quiet
However, underage drinking in pubs was rife with ID cards being non-existant. Managing to get a pint at 16 or 17 was a sought after goal seen as a coming-of-age badge-of-honour, goals I scored repeatedly being tall and prematurely rugged at that tender age.
Back then there was an amusing TV advert for Whitbread Trophy Bitter featuring the actor Brian Glover taking his just-turned-18 son for his ‘first pint’ and giving him fatherly advice like ‘take it slowly, don’t rush’. On entering the pub the locals welcome the lad with an ‘evening [name], brought the old man for a pint have you’. Wouldn’t pass the censors now 
There’s numerous old beer ads on Youtube but I couldn’t find that one unfortunately.
As for children in pubs nowadays I agree with Corker’s wet-pub food-pub rule.