(No, I don't know what "Genre wheeze" is, nor how it can be cured. When I was growing up a "wheeze" was, in the comics anyway, what Baldrick might have called "a cunning plan", but I think this particular wheeze is probably asthmatic.)
(Personally, I think it's more probable that reviewers have an easier time with Coraline than with the adult fiction because no-one expects kids' books to be "realistic" by default. They're already marginalised into a genre -- they're Children's Books, and they exist within a comfortable tradition of imaginative literature, what Clive Barker used to call the fantastique. But it may also be because Coraline's a better book.)