Another book I've reviewed before, but I enjoyed rereading Cornelia Funke's The Thief Lord. I like its depiction of Venice (an Italian city I've not seen but wish to visit). The child characters are all interesting. Bo's childish behavior (he's five) is realistic for a kid that age, and it also allows him to be a very useful plot advice from time to time. Prosper is a straight man character, pretty serious for a twelve-year-old, trying not to give in to thieving and always doing his best to be a mature and moral example for his little brother. I also liked Hornet, who didn't suffer much from being the token girl. Scipio was kind of annoying, but then he's supposed to be a pompous, if good-hearted, kid who thinks he knows more than he does and fancies himself practically an adult. The adult characters are just the sort you want for a story with young protagonists who operate outside the mainstream. Victor and Ida are unconventional but not irresponsible, and you end up rooting for them as well as for the kids.
The plot itself is pretty simple, and for all the book has a very magical feel to it, except for one element late in the book, everything is actually very mundane. Kids running away from relatives because they're unhappy, orphans who steal to survive, a private investigator who works to pay the bills, an an eccentric photographer. But the way they're combined gives one suspenseful, hushed feeling to the whole story.