His other books - novels tackling complex issues such as race, American identity and hip-hop culture - took considerably longer to write and haven't been as lucrative as the two spoofs on parenthood. But Mansbach says the common thread in all of his work is honesty. He would never have written had he not been a parent himself and feeling a little flummoxed at taking care of his daughter.

"The paradox of parenting is that there is constant discussion of it everywhere you look, but it's not always the most honest discussion," he says.

"There are things that are taboo to talk about, and one is the level of frustration we feel as parents, because we feel like if we talk about it, we're bad parents … it's breaking the script of what you're supposed to feel as a parent."

Mansbach suggests it's this truthfulness that turns many grandparents into an important part of his fan base. "Any time the book has been criticised [for the swear words], grandmothers defend it immediately," he says.

"Sometimes we assume that older people are going to be prudish or afraid of bad language, but they've raised kids, too, and a lot of them were like, 'I wish this had been around when I was raising my kid.'"

Audio versions of the books, narrated by American actors Samuel L. Jackson and Bryan Cranston ( ) and English comedian Stephen Fry, have gone viral. A clip of Cranston reading notched up more than one million views on YouTube within a few days.

However, Mansbach's favourite is a reading by a Filipino woman whose daughter gave her to read to her grandchild: "She's really embarrassed but she keeps reading and laughing; she's like 'this is so bad' but she keeps going."

Coming from a family of writers (his grandmother was a poet, and his parents were journalists), Mansbach says they are generally comfortable around profanity and simply regard it as an instrument in the writer's toolbox. He has even introduced Vivien, now 6½, to recordings of his books.

"She's old enough now … and she's cool about profanity - it's not taboo but it's also understood that [swearing is] not appropriate either. So I can play her the book and be like 'Viv, I'm going to let you hear the swear words, you know not to go to school and say them, right?' She gets it."

Mansbach has the same philosophy about drinking: if his daughter wants to try some beer after she turns 16, he'll gladly give her some at home because it's better for her to understand that alcohol is something that has to be consumed in moderation or limited quantities. That approach connects the spoof children's book to his other work.

"I never envisioned writing [ ], but it does come from the same aesthetic as my other work as a novelist in that I'm very committed to telling the truth - telling uncomfortable truths."

Mansbach developed that approach to life early on, through his fascination with hip hop. He started rapping as a 10-year-old, ran a hip hop magazine in New York in the 1990s, and says the culture and politics of hip hop have shaped him.

"Hip hop was forged by people who had been disempowered by the city they lived in - young black and brown people in New York in the '70s. The city was engaging in a policy they called Benign Neglect, which was 'Let those neighbourhoods crumble'." That led to "all kinds of repressive and racially biased systems of policing and of municipal government", Mansbach says.

"Music became political, it became a coded way to speak and speak truth to power. When I was a kid, it was the most honest place you could go for a discussion about race and racism. Those were taboo topics in a lot of places.

"Hip hop was honest about it. Hip hop talked about apartheid in South Africa and Euro-centricity in education and police profiling and police brutality," he says.

Mansbach's faux children's books have opened new doors for him even as publishers continue to struggle. The surprise success of in 2011 came at a particularly opportune time: his job teaching fiction writing at Rutgers University was about to end and he was moving back to California into a house he had bought "but couldn't quite afford". When the book took off, options opened up for him: an audiobook collaboration with Samuel L. Jackson yielded an invitation to write a campaign ad for US President Barack Obama in the 2012 elections, which the actor also narrated.

Mansbach has since published , a novel about graffiti artists in New York. Although editors have said that they love it, he believes publishers might not have given his book the go-ahead if he weren't already established.

"You can put No1 bestselling author on the cover of anything I write now," he quips. His bestseller might have nothing to do with the current project "but it still helps".

He's now writing a movie adaptation of , a children's classic that he loves, and another director has hired him to write the screenplay for a new film.

Meanwhile, Mansbach tries to cope with his daughter Vivien's constantly evolving food preferences; it's all he can do to keep up, he says.

"My daughter is awesome, I'm very proud of her, she's a really cool kid, but the absurdity is that you're both all powerful, and also totally at the mercy of this little creature."

Yet he suspects that someday he willl miss the everyday parenting struggles.

Recalling a conversation he had with a passenger on a flight several years ago, Mansbach says: "His kid was away at college and he said he missed changing diapers. I was, like, 'You're crazy man; are you drunk right now?'

"But I'm beginning to see how something like that could be possible."