A seven-week-old baby died because his mother or father “inadvertently rolled on to him” when they were sleeping, a High Court judge said.
Mr Justice Keehan said health workers “repeatedly” warned the couple about the dangers of sleeping with babies.
The parents, who have three other children, live in or near Birmingham and cannot be identified.
The judge said the baby, who suffered multiple rib fractures, had not died as a result of any intentional act.
On the night the baby died in March 2019, his father had taken cocaine and his mother was “extremely tired” and “under the influence of alcohol”.
Mr Justice Keehan concluded the baby died as a result of asphyxia because his mother or father inadvertently rolled on to him while asleep, or because he had been “confined in a micro-climate” where the atmosphere was low in oxygen but high in carbon dioxide.
He said: “The mother told me that co-sleeping with her children had worked for her and for the father, they had regularly pursued the practice with all of their children.