This question already has an answer here:
Flags on child meta sites are only shown to the site's mods when they visit meta. On sites whose metas are not very active, this means that it could be several days before a mod notices the flag.
Could we please have a centralized flag menu? I would like to see both meta and main site flags appear in the same place irrespective of which site I happen to be browsing at the time. Perhaps they could be color-coded so that we can know what site (meta or main) they're coming from, but at least, they should all appear in one place.