People that mostly like their kids and kids in the abstract, but nonetheless want to complain about some aspect of kids (understandably!), may not wish to create the impression that they're not into their kids. So they make sure to include a disclaimer in their complaint that their kids are wonderful, etc.
It's different among close friends -- there you find people complaining that their kids kept them up all night or whatever without feeling the need to include a "my kids are wonderful" every third sentence. Because their close friends know this implicitly.