Learn Swedish: Diagrammet visar åldersgruppen, varav många är barn. - The chart shows the age group, of which many are children.

varav translates to 'of which' or 'out of which' and is used to introduce a subset of something previously mentioned. While you could grammatically say av vilka (of whom) since it refers to people in the age group, varav is the standard, more elegant choice in written Swedish for expressing proportions or subsets.

Does varav trigger a specific word order in the clause that follows it?

Yes, varav is a relative adverb that introduces a subordinate clause. In this sentence, många is the subject and är is the verb. If there were a sentence adverb like inte, it would have to go before the verb according to the Swedish subordinate clause rule (the BIFF-rule), making it varav många inte är barn.

Why is there an extra s in the middle of åldersgruppen?

That is a connecting s. When joining two nouns to form a compound noun, an s is often inserted between them, especially if the first word ends in certain suffixes like -er (from ålder). It acts as glue between ålder (age) and gruppen (the group).

Since åldersgruppen is a singular noun, how can många (many) be extracted from it?