I have been reading BBC news for a long time and one thing attracts my attention on the texts, because that type of usage clashes with what we were taught on relative clauses, e.g. "30 people died. Most of them were children". You normally combine these sentences "30 people, most of whom were children, died".
But in the BBC news texts, they do not combine the sentences like this. Instead, they put the second sentence between commas and removing "are". But it is not a relative clause, at least in the sense what we are taught in English classes.
See the following BBC sentences for more details and focus on "...most of them children..."
1- "...The year before, a passenger ferry capsized and more than 300 people died, most of them school children on an outing..."
2- "...More than 140 people, most of them children, were killed when Taliban gunmen stormed a school in Peshawar, Pakistan, officials say...."
3- "...More than 140 people, most of them children, were killed when Taliban gunmen stormed a school in Peshawar, Pakistan, officials say...."
You see, they do not make a relative clause like we are taught at school which should be like this: "...most of whom were children...".
So, What kind of a clause is this? Or is it a relative clause at all? If it is not, what is it? Is it correct?