The court heard the Yasharahyalahs had been motivated by a belief system including a restrictive vegan diet and a desire to avoid unwanted attention and, the prosecution said, were prepared to allow their child to "suffer the consequences".
The parents had believed Abiyah would be reincarnated if they followed a burial ritual, the jury heard.
Yasharahyalah said in his Igbo culture it was believed every person had a physical and spiritual form, the latter of which could be saved.
The pair did not call the emergency services after Abiyah died because strangers could scare off spirits. Instead, they lit a paraffin lamp in the room near him as a beacon, in case his spirit wished to return to his body.
After an eight-day period, his body was embalmed, and they buried him in the garden.
Asked if they had buried the body to hide it, Tai Yasharahyalah said it was "not the case at all".
Following the verdicts, the judge, Mr Justice Wall, commended jurors for their work and said it had been "both a long and difficult case".
The couple showed no visible or audible reaction to the verdicts.