Depends, uk licensing laws are complex... for example a pub with an area set aside for serving a substantive meal may be permitted children in those areas only if they are eating with adults.

A restaurant with a pub/bar attached, even if completely openly attached so looks exactly the same as the pub example above, will almost certainly be permitted to serve children food without an adult present (at least legally, some may have policies against that).

And those are the easiest examples.