The (parental) doubt is quite justified, because the MCU is known for diving into a new genre with every film (or series). That makes the thing – or rather: the universe – exciting, of course, but also difficult to assess. Which adventures from Iron Man, Thor and Black Widow can I expect my children to have, which ones might give them nightmares or overwhelm them?
In principle, all Marvel films and series are marked with FSK 12, i.e. officially approved for ages 12 and over. But what would kindergarten and elementary school be without Spidey, Captain America and Co.?