Former teacher Jamie Varley has been found guilty of the murder, sexual assault, infliction of grievous bodily harm, and four counts of child cruelty relating to 13-month-old Preston Davey.
His partner, John McGowan-Fazakerley, was also found guilty of allowing the death of a child, child cruelty, and sexual assault.
The couple were in the process of adopting Preston.
Just four months after being placed with them, Preston was taken to hospital unconscious and in cardiac arrest. Despite efforts to save him, he died.
They will be sentenced on Thursday, 18th of June at Preston Crown Court.