Mr. Smith: I would suggest that ведь can be translated as "after all, as we're both aware..." or "since we both know" or "considering that it's common knowledge that..."

In other words, it introduces something that the speaker assumes is already known to the listener. Thus, in #9 and #10, the writer is basically saying "it's not surprising that St. Pete's has so many canals, since, after all, even a child is aware that the city is built on more than 100 islands."

P.S. As far as I know, ведь is always unstressed in speech, which means that the -е- is vowel-reduced and you pronounce it "вить".