A 13-month-old baby drowned in a bath at his home while his parents were downstairs, a jury has been told.

Kian Dale had been left in a bath seat at home in Kyreside, Tenbury, while his parents Wayne Dale and Lisa Passey were downstairs smoking cigarettes with a friend, Worcester Crown Court heard.

When 44-year old Dale went back upstairs to get Kian he found the baby slumped over lifeless in his bath seat with toys floating in the water, Jonas Hankin, prosecuting, told the court.

Efforts to resuscitate him failed and he was found to have soap bubbles in his lungs when he was examined at hospital.

Dale, now of no fixed address, and Passey, aged 28, of Kyreside, both deny manslaughter due to gross negligence.

Mr Hankin said Kian had been put in the bath in a seat connected through a central pillar to the bottom of the bath by a suction cup at about 5.30 pm on the evening of September 28, 2015.

Passey had put water in the bath and then gone downstairs to see a friend.

Dale also went downstairs and rolled a cigarette and joined them at the outside doors to smoke.

They were playing music by UB40 and their visitor asked Dale to burn her a CD, Mr Hankin said.

He agreed and evidence from his computer showed he had accessed it between 5.33 pm and 5.46 pm.

Passey asked him to go back upstairs and he found Kian lying in the seat, which was capable of a swivel movement.

"He scooped him out of the bath and took him downstairs," Mr Hankin said. "There were no signs of life."

Passey said "time had got away from her" and she had not realised they had been downstairs for so long.

There were safety warnings with the bath seat but Dale and Passey had chosen to put their own convenience ahead of the child's safety, Mr Hankin said.

He told the jury the couple would be blaming each other but it was the responsibility of them both as parents to make sure Kian was safe and to avoid a catastrophe because babies did not have a sense of danger.

They had a duty of care and there was an obvious risk of drowning, Mr Hankin said.

He told the jury the offence carried an objective test.

"Would you leave a 13-month-old baby in a bath with water?" he said.

"If not, why not? And if the answer is obvious then the objective test is met."

The trial continues.