Hillary Clinton targets Donald Trump in new ad

Donald Trump is at the centre of attack in a new advertisement by the rival Hillary Clinton campaign that invites adults to imagine what a child might be learning from the Republican presumptive nominee's provocative rhetoric.

Soft, inviting piano tones are set against a pink sunset and a neighbourhood at dusk, before the 70-year-old real estate tycoon's voice interrupts the tranquil scene.

"I love the old days. You know what they used to do to guys like that when they were in a place like this? They'd be carried out on a stretcher, folks," Trump is heard telling a crowd.

More of his acidic comments are played, while the screen is filled with close-ups of children gazing at television sets, seemingly soaking up every R-rated remark, the New York Times said in a report.

"Our children are watching," a text card warns after two young children watch on television Trump appearing to mock a reporter with a disability.

At the end, Clinton is shown delivering a speech on children, closing with: "We need to make sure that they can be proud of us."

The ad paints Trump as "unpresidential and unfit for office, in the eyes of both children and, the ad assumes, their voting parents (who, one could argue, might not be too happy with the Clinton campaign's rebroadcasting of the messages to children watching television)," the NYT report said.

It added that the Clinton campaign has also made the 68-year-old former secretary of state's record of working for children and families a central focus, while trying to portray Trump as a poor role model for children.

While the underlying message feels familiar, the timing is important as Trump heads into the Republican National Convention and is set to enjoy several days of free, unabated media coverage, often in prime time and perhaps when children are watching. The Clinton campaign can counter with a paid message placed strategically in the coverage, it said.