A mother chose to protect her partner after he fatally injured her three-year-old son rather than seek emergency medical help, a jury has been told.
Riley Siswick was found dead two days after he was seriously injured by Kyle Campbell, 26, at their Huddersfield home, prosecutors told Leeds Crown Court.
Robert Smith QC, prosecuting, said neither Riley's mother, Kayleigh Siswick, 26, nor Campbell raised the alarm about the youngster's acute and deteriorating condition which "would have been obvious" to anyone.
Mr Smith said Riley was injured in his abdomen by Campbell on Thursday February 4 2016, "either from a fist, or by jumping or stamping on him or by striking him with an object".
The prosecutor told the jury the blow had injured Riley so severely that it caused peritonitis - a life-threatening infection.
Mr Smith said this would have caused severe pain which "would have been obvious to the person who caused the injury or any adult who saw him after the injury was sustained on Thursday afternoon".
He said the boy would have deteriorated and developed septic shock.
The prosecutor said Riley eventually died from the peritonitis and hypovolemic shock due to fluid loss.
"His situation was a medical emergency," Mr Smith said on Wednesday, "His deteriorating condition would have been obvious to both defendants.
"Why, at any time from that Thursday onwards, neither of the defendants telephoned for medical help or took him to accident and emergency at the local hospital."
Mr Smith said Siswick failed to seek medical help for her son and "instead, she chose to protect Kyle Campbell".
He said paramedics were eventually called to the house on Smiths Avenue, Huddersfield on the morning of Saturday February 6, but Riley was already dead and had been for a number hours.
The prosecutor told the jury the prosecution case was that Siswick was out of the house when Campbell injured her son.
But he said there was evidence that Siswick knew Campbell had injured her son before and she would have been aware that he was capable of hurting him again.
The prosecutor said that when paramedics arrived at the house after Campbell called for an ambulance, Siswick said "why didn't I check on him" and "we just found him like this".
He said the defendant told the medics her son had been suffering from diarrhoea and vomiting.
Campbell denies murder and causing or allowing the death of a child.
He also denies two counts of causing actual bodily harm.
Siswick denies causing or allowing the death of a child.
The case was adjourned until Thursday.