A man has been jailed for life for murdering his girlfriend's two-year-old son at the family home in Birkenhead.
Craig Smith, 28, used "extreme violence" in attacking Teddy Tilston, who had injuries to his head, ear, upper lip, neck, jaw, abdomen and back.
He was also convicted at Liverpool Crown Court of causing actual bodily harm to Teddy's twin sister.
Smith and the children's mother, Ashleigh Willett, 25, were also found guilty of two counts of child cruelty.
The jury took 19 hours and 11 minutes to reach their verdicts.
Smith will serve at a minimum of 17 years in prison while Willett will be dealt with at a later date.
Paramedics arrived at the couple's home in Woodville Road, on the Wirral, on 1 March to find Teddy lying on the floor in a nappy and vest.
Smith claimed the toddler drowned in the bath, despite being completely dry when ambulance staff saw him.
He showed no signs of life but the court was told that a brain injury caused by a lack of oxygen suggested he had survived at least 30 minutes after being injured.
The jury was told that a post-mortem examination found that the fatal injury was an internal tear to tissues joining the wall of Teddy's abdomen, likely to have been caused by abuse.
Prosecutor Nicholas Johnson said: "The bottom line was that Teddy did not drown. He was punched or kicked in the abdomen."
Willett had sobbed while giving evidence as she was taken through the lists of injuries suffered by each child.
She had been at work while Smith looked after the twins and their older sister.
Det Ch Insp Paul Denn, of Merseyside Police, said: "The death of two year-old Teddy Tilston was a senseless tragedy.
"Craig Smith, as the partner of Teddy's mum, was the man given the responsibility of looking after Teddy and his twin sister which makes this whole situation even more shocking."
An NSPCC spokesperson said: "Teddy Tilston was murdered in the most shocking and brutal fashion by a man responsible for his care and protection.
"It is heart-breaking to imagine the pain Teddy suffered and to think that he was powerless to escape his circumstances."