I'm a little confused about what you're asking... nightclubs that serve food? Or nightclubs that ID minors?
The thing about pubs, nowadays, what you said is true, and especially since the economic downturn. Most pubs serve food otherwise they just wouldn't survive. However, going back even ten years or so, there'd still be a fair few pubs that didn't serve food, didn't allow children past a certain time, or at all.
However, I first went into a pub on my own when I was about ten or so (around 2000), so pubs did allow children in (we only went in to get chips at lunchtime when we helped at the riding school) but going back a few decades, that would never have happened. My dad always used to tell us about how he didn't set foot in a pub until he was either 16 or 18, can't remember which. He was born in 1960, so if you're setting your story around that sort of time, serving food in pubs to minors was probably not done.