That being said, reading about realistic - and flawed - characters gives me a look at a world I don't normally see, and makes me appreciate what I have in my life: No kids, no drama. There is definitely a place for that in fiction.
The further I got into the story, the more I was drawn in, and I actually stayed up pretty late a few nights, reading more than I had intended. I had to see what was going to happen next - how would Mallory deal with the next crisis, and would she get caught snooping around her employer's house? And most importantly, would any of them grow out of their poor behaviors? (Spoiler - they do! Which makes it totally worth all the cringe-inducing moments.)
I found the story arc believable, the characterizations solid, and the character growth timed to perfection. The characters - with the possible exception of the mother - were totally redeemed in my opinion. Their poor behavior lasted no longer (nor shorter) than necessary to be believable and compelling, and there was just cause for every turn and bump in their interrelationships. (Any faster and it would have been too easy. Any longer, and a sane person would have given up.)
So why not 5 stars? Well, the ending was quite abrupt. We weren't given a real sense of what the future would really hold for everyone. I did like the building relationship between Mallory and Brendan, but I questioned their declaration of love for each other at the end. I could definitely see it building toward that end, but I didn't quite think she had enough to go on to love him. Of course he would love her, but since he was a jerk for most of the book, I'd prefer to see her waiting to see that he was really mending his ways. I also had a bit of trouble with...not their age difference, per se, but the way Mallory is so often described as a "girl." It just made it hard to see her as a potential love interest for Brendan when so often it felt like she and Meela were being described as though they were sisters. And finally there were a few style choices that I found jarring. Not really errors, just small things that jarred me out of the story a few times. So, I'll have to leave it at 4. Maybe 4.5
As for content, this is a sweet, clean story. Probably PG, but only for some references when Mallory and Rashelle are talking to each other. There's no swearing, no hanky-panky, and no major violence - although there are references to a rough childhood for Mallory, a couple run-ins with the schoolyard bully, and some speculation as to what really happened to Brendan's wife. Don't take that to mean the story is dull, though. There are a couple exciting scenes, and plenty of drama.
All in all, I recommend The Nanny Song as a fine clean read.