The children used in FNB's "You Can Help" ad campaign were paid and the videos, which contained negative opinions about government, were scripted.
The New Age reported on Tuesday that the videos were scripted and that the children were paid R3 500 a day to appear in the videos.
The campaign features a number of videos of children in school uniform reciting their hopes for the country.
First National Bank's (FNB) chief marketing officer Bernice Samuels reportedly told the newspaper it was industry standard to pay performers in an advertisement. Last week, FNB said an independent company had surveyed youth aged 10 to 22 to understand who they were and how they felt about South Africa and its future.
The bank said they were told they could talk freely, without fear or favour, and that "unscripted and uncensored" videos used in the campaign emerged from this process.
But Samuels reportedly told the New Age that while the casting interviews were "unscripted, uncensored and very much from the heart", the final advert was scripted and was approved by the bank's marketing team.
According to the New Age, a call sheet from Take Ten Casting confirmed "the advert was in no way a spontaneous or natural gathering of young South Africans", but that each participant was "carefully selected".
The campaign was met with anger from the ANC, which said the adverts were a "political campaign" and an "attack on the president".
FNB met ANC leaders, including secretary general Gwede Mantashe, about the adverts on Thursday, and apologised to the party on Friday.
During the meeting, the ANC reportedly argued the campaign sought to project the party and government in a negative light. The ANC said the clips impacted business confidence negatively and could undermine investment in the country.
Opposition parties and activist groups said the ANC's criticism of the campaign showed its intolerance.
FNB also took out full-page advertisements in four national newspapers last Sunday. The text of the adverts, published in the Sunday Times, City Press, Sunday Independent, and Rapport, appeared in five stanzas, each beginning with the line: "We help because we believe".
It concludes with the words, in bold type: "We help because we believe where there's help, there's a way." – Additional reporting by Sapa