The boys, aged 13, 15, and 16, are among those charged with possession of a Class A drug with intent to supply.
Fifteen people have been remanded in custody and are due to appear in court on Thursday.
Gwent Police raided 35 addresses in the city and made 25 arrests. Three people have been released with no charge and two are awaiting questioning.

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The four-time Olympic champion returned to the velodrome last year in a bid to qualify for his fifth Olympics.
"It's an evidence-based selection he's involved in," Sutton told BBC Sport.
"Brad has to go out and produce in London which will determine whether he makes the road to Rio or not."
Wiggins, 35, is set to team up with Mark Cavendish in the non-Olympic madison at the Worlds, which run from 2-6 March and will be broadcast live on the BBC.
Wiggins, who has won seven Olympic medals on the track and road, will also race in the four-man team pursuit, which is his target for Rio.
As for Cavendish, who partnered Wiggins to win the madison at the 2008 World Championships, the 30-year-old aims to represent Britain in the six-event omnium at this summer's Olympics.
"As things stand right now, he'll be on the start line in London," Sutton said of Wiggins.
"There are six guys in the mix at this moment in time. Brad's one of the strong guys in that group."
Sutton believes that the 2012 Tour de France winner can rise to the occasion in front of a home crowd.
"Like everybody else, Brad is definitely under pressure, but Brad's the ultimate professional," he said.
"Brad would de-select himself if he didn't think he could do the job, but I'm quite sure he can."
Sutton added that selection for Rio was far from settled.
"There's a foot in the door for anybody who goes to London," he said.

Police said 26-year-old Bamilola Kazim was allegedly assaulted by Mohammed Gafoor after a row on Wednesday
Mr Kazim was treated for wounds at a local hospital and released.
Last week a student from the Democratic Republic of Congo was beaten to death by a group of Indian men after an argument in Delhi.
Two men have been arrested in connection with the killing of the Congolese man.
Indian foreign ministry spokesperson Vikas Swarup  tweeted on Friday that Foreign Minister Sushma Swaraj "had urgently sought report" on Wednesday's incident from the local government "and is monitoring the case".
Police said Mr Kazim allegedly parked his car in front of Mr Gafoor's house, and was attacked with an iron rod by the latter after an altercation.
"We have arrested the accused and the matter is now in court," Hyderabad police officer K Krishnaiah told BBC Hindi's Imran Qureshi.
Gideon Omodowale of the local Nigerian Students Association said it was a "racial issue".
"If he was a US citizen or an Indian, he wouldn't have been attacked. Later, some community people came and he [Mr Gafoor] apologised. We are ready to drop the case because we don't want it to affect other Africans," he told the BBC.
There are more than 4,000 students from African countries in Hyderabad.
Following last week's killing of an African student in Delhi, a group of African embassies had said they did not want to participate in Africa Day celebrations on Thursday because of repeated attacks on African students in India.
They relented after Ms Swaraj promised to ensure the safety of African students in India.
Mr Swarup said the Indian government had received news from its embassy in Kinshasa, the capital of Democratic Republic of Congo, that some "Indian establishments and shops were attacked on 23 and 25 May as a reaction perhaps to the killing of the Congolese national" in Delhi.
"It has been reported that by Wednesday, things have calmed down," Mr Swarup was quoted as saying by The Hindu newspaper.
Authorities in the Democratic Republic of Congo have not yet commented on the remarks.
In February, a Tanzanian student was assaulted and partially stripped by a mob in the southern city of Bangalore.
Twenty people, including three teenage boys, have been charged following a drugs raid in Newport on Wednesday.
[NEXT_CONCEPT]
Sir Bradley Wiggins "must produce" at March's World Championships in London if he is to make the track team for the Rio Olympics, says British Cycling's technical director Shane Sutton.
[NEXT_CONCEPT]
India's foreign ministry says it is looking into an alleged attack on a Nigerian student by a local man in the southern city of Hyderabad.