The 31-year-old singer is said to have secretly listed the advert but gave away her identity with a series of huge clues.
Charlotte's supposedly wanted ad indicated that a "well-known singer" was looking for a nanny to help with "washing, shopping, nappies and two dogs" and that both parents in the "VIP family" are musicians, The Sun reports.
It also described her as a "super laid-back mum" wanting the nanny to do "fun, cultural and educational activities", based at a home near Cardiff which has a recording studio at the property, the website claims.
The recruitment ad is also said to state that the mum is expecting her third child in November.
WENN • ITV
Charlotte Church was ridiculed on Twitter after being rumbled placing an advert for a nanny
Charlotte is reported to have placed the advert secretly
She recently appeared to announce her pregnancy live on stage
Several people took to social media to ridicule the politically active star for her apparently failed attempt to keep her identity hidden, with one tweeting: "Charlotte Church considers herself a VIP when advertising for a nanny… after all her campaigning good to see she's one of the people."
Another shared an article exposing her, adding: "Beyond thick…"
"'Loony activist' would have given it away," a third Twitter user quipped about the seemingly obvious clues in the advert.
Although she hasn't officially confirmed the news, Charlotte seemed to reveal her pregnancy during her gig last weekend, as she cradled her bump throughout her performance.
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Charlotte is thought to be expecting a new arrival with her boyfriend Jonathan Powell
People took to Twitter to ridicule her for her apparently failed attempt to keep her identity hidden
She is thought to be expecting the new arrival with her musician boyfriend Jonathan Powell, after the pair starting dating in 2010.
Charlotte already has two children, Ruby, nine, and Dexter, eight, with her ex-fiancé and rugby star Gavin Henson, 35.
The star previously spoke out about her relationship with Jonathan, admitting that she hadn't "ruled out" expanding their brood.
Several people tweeted about the advert for a nanny for the 'VIP' family
Others mocked Charlotte's attempt to conceal her identity in the ad
"I'm really happy with my dude," she told The Telegraph last year. "He's lush, he's so smart and he really looks after me.
"I don't know. I'd never rule out anything. Never say never!"
Express.co.uk has contacted a representative for Charlotte Church asking for comment.