One infant is being reared in "appalling" conditions in Brazil and another new-born British baby is in prison in France.
Two more babies are due to be born to young British mothers jailed in Morocco and Brazil.
Prison support groups have warned the Foreign Office that the babies are susceptible to potentially fatal illnesses because of the appalling jail conditions.
Rhys Brown, eight weeks, is the youngest of 1,800 British citizens incarcerated overseas.
He was born on August 26 to 19-year-old Jessica Rowllings, from Colwyn Bay, north Wales. The pair live in Bordeaux central prison in France. Their cell on an upper floor with a small barred window, has its own cot and toys for the baby.
Rhys is visited for half-an-hour, once a week by his father Elliot Brown, 21, who is held in the same jail. Brown is not allowed to touch his girlfriend and son and must talk across a table. The couple were arrested in February for speeding as they headed home from Spain. Police found a large quantity of hashish in their car.
Brown was sentenced to six years and Rowllings, who said she had no knowledge of the drugs, was given two years. She was three months pregnant when she was arrested, was also fined pounds 350,000.
Last night, Ms Rowllings' sister, Maeve Smith, from south London, said that the French authorities had told her sister that she could be released if she paid pounds 17,500 of her fine.
"Even that is way beyond the family's means. This is all so cruel. Jessica said she knew nothing about the drugs and she has never been convicted of anything before," Ms Smith said.
She added that when Rhys reached the age of 18 months the French authorities would decide whether to place him with French foster parents or send him to relatives in Britain. She said: "Seperating Jessica from Rhys would be cruel beyond belief. We think they should both be brought home together."
In Brazil, there is great concern for the welfare of a 21-month-old baby being brought up by a British woman in Rio de Janeiro prison. The mother, in her 20s, has been convicted of drugs trafficking.
The Foreign Office last night confirmed that another British drugs carrier, held in Sao Paolo prison, Brazil, was four months pregnant, having conceived her baby while in jail.
In Morocco, Sally Griffiths, 18, learned she was pregnant two months after being sentenced to five years for drugs smuggling. Moroccan authorities said that when the baby is born in April she can either hand it to relatives or keep it in prison until the age of two. At that point she must send the child to her family in Britain.
Griffiths was arrested in July along with her friend Claire Martin. They were convicted of trying to smuggle cannabis worth pounds 23,000 from Morocco to Amsterdam.Carlo Laurenzi, director of Prisoners Abroad, the charity that helps Britons jailed overseas, said: "These babies face a high risk of pulmonary infection and disease. In countries like Brazil and Morocco, the prison authorities are simply not geared up for births. We would like the early release of these women to give their babies a better chance of survival."
Prisoners Abroad is especially concerned about the terrible jail conditions in South America which have already claimed the lives of several British adults.
Last month Raj Sidhpura, a British citizen, died in a prison in Rio de Janeiro shortly after making a desperate plea to Malcolm Rifkind, the Foreign Secretary, about his prison conditions.