Angharad Williamson, 31, John Cole, 40, and a 14-year-old, who cannot be named, killed Logan Mwangi in July 2021.
Logan’s body was found in the River Ogmore, close to his home in Sarn, Bridgend county.
He died after suffering a “brutal and sustained” attack at home, leaving him with “catastrophic” injuries.
The prosecution said Logan’s body was dumped in the River Ogmore on 31 July like “fly-tipped rubbish”.
Police officers found the schoolboy partially submerged in the water wearing a pair of dinosaur pyjama bottoms and a Spider-Man top just 250 metres from his home.
The youngster had 56 “catastrophic” injuries, including extensive bruising to the back of his head and tears in his liver and bowel, which experts said were so severe they were consistent with those seen in road traffic accidents.
Experts also said the injuries could have only been caused by a “brutal and sustained assault” inflicted on Logan in the hours, or days, prior to his death, adding the injuries were “consistent with child abuse.
During the trial, the jury were played extensive CCTV footage from nearby houses around the time of the incident.
Cole and the teenager were seen at 02:43 BST on 31 July moving Logan’s body to the nearby river where they dumped it.
They were caught again as they came back to the house to pick up the dinosaur pyjama top Logan had been wearing to take to the river, which police found in a wooded area with a big cut in.
Williamson told the jury she was asleep all night, but CCTV showed the lights going on and off in Logan’s room and the curtains being opened.
There was also evidence showing she had used her phone at time to watch videos on YouTube.
The jury were also played a frantic 999 call from Williamson recorded hours later telling police her son was missing.
They were also shown bodycam footage from police who arrived at the house shortly after, where Cole appeared to be comforting a distraught Williamson.
All of this, the jury found, were lies.
Cole had already pleaded guilty to perverting the course of justice after he put Logan’s body in a sports bag and dumped it.
Williamson and the boy also denied perverting the course of justice but were found guilty.
Cole, Williamson and the teenager had all denied murder, but were found guilty following a trial.
The two adults pleaded not guilty to causing or allowing the death of a child.
