A foster mother who called her baby a "moaning whinge bag" before killing the one-year-old had told social workers she did not love him.
Laura Castle, 38, was on Tuesday found guilty of murder at Preston Crown Court after claiming that Leiland-James Corkill had fallen off the sofa and hit his head.
The child had been placed with Laura Castle and her husband, Scott, 35, by authorities in Cumbria less than five months before his death.
Leiland-James was a "looked-after child" who was taken into care at birth before he was approved to live with his prospective adoptive parents from August 2020.
Laura Castle rang for an ambulance on the morning of Jan 6 2021, saying Leiland-James had fallen off the sofa and was struggling to breathe.
However, hospital doctors raised concerns as the extent of his injuries did not match her account.
Leiland-James died the following day as Castle maintained to police, as well as to family and friends, that the death was a tragic accident while her husband, a night shift worker, was asleep.
She stuck to her story until the day the jury was sworn in for her trial in April, when she pleaded guilty to manslaughter.
Her new version of events was that she had shaken Leiland-James after he had not stopped crying at breakfast and his head hit the arm-rest of the sofa before he fell off her knee on to the floor.
However, medical experts told the court that the degree of force required to cause the baby's injuries would have been "severe" and likely to be a combination of shaking and an impact with a solid surface.
Prosecutor Michael Brady QC said it was the Crown's case she killed the boy as she lost her temper and suggested she smashed the back of his head against a piece of furniture.
The former care worker denied intending to kill Leiland-James or seriously harm him but jurors took just two-and-a-half hours on Tuesday to convict her of murder. She was also convicted of child cruelty.
Sentencing will take place next Wednesday.
Scott Castle, who worked as a machinist at defence firm BAE Systems, was found not guilty of allowing Leiland-James' death. He was also cleared of child cruelty.
Trusted his wife
He said he never had any concerns that anything bad was going to happen with the boy and he trusted his wife.
The Castles had been selected by an adoption panel following an application process overseen by Cumbria Children's Services Department, the court heard.
In Nov 2020 concerns were raised that Laura Castle had said during a home visit she did not love Leiland-James and was struggling to bond with him.
The following month, the Castles were told by a senior social worker she would not support any application to formally adopt Leiland-James and recommended further therapeutic parenting sessions.
The possibility of removing the baby from their care was raised, but Laura Castle said her extended family loved him so he was "not going anywhere".
Concerns remained about the lack of emotional bond, the court heard, and a review by social services was set to take place early in 2021.
Detectives found text messages sent to her husband which referred to the baby as "a proper k--- head", "a d---" and "a s--- bag", while her husband said the baby was "a fat s---", "a k--- head" and "a toss bag".
Laura Castle said the texts reflected her "sense of humour" and should not be taken literally, while Mr Castle said he was now "ashamed" at sending the messages but he did not mean malice and was trying to sympathise with his wife.
She messaged on several occasions that she had "leathered" Leiland-James, although she told the jury that only meant smacking.
In one exchange in Sept 2020 she wrote: "I'm seriously at my wits end, no one tells you about all this s---. I'm just an abusive parent so it seems."
Mr Castle responded: "Your not an abusive parent, baby. Not at all. Don't say that. I think he's a little too f----- up for us to handle.
"Let's just call it quits. I don't want you to have a mental breakdown. Your more important to me than him."
Scott Castle no longer works for BAE Systems, the company said after the hearing.
Cumbria County Council said an independent review was taking place into the case and is due to report back in July.
John Readman, the council's executive director for people, said: "Adoption should have been a new beginning for Leiland.
"That was cruelly taken away from him by the person who should have cared for him and kept him safe.
"We are deeply sorry for Leiland's death, it should not have happened.
"Our thoughts and sympathies are with his birth family and all those who knew this little boy.
"Abuse of a child by adopters is almost unheard of and we are determined to do everything we can to prevent this happening again, here or anywhere else."