It all changed in 2003.....there's no age restriction for accompanied children in licensed premises. Unaccompanied youngsters have to be 16 or over in wet-led pubs. Though pubs can of course have their own rules, like no one under 21, and restrictions can be applied by councils to premises licences
There's a reasonable account here:
https://www.nwleics.gov.uk/files/doc...n/Children.pdf