Children in French overseas territories lack the access to healthcare, housing and education that those in mainland France can rely on, according to Unicef, reports Radio France Internationale.
The UN children's agency is calling on the French government to address what it calls "alarming inequalities" and protect basic rights across the country.
In its report "Growing up in the overseas territories", Unicef flags up stark disparities between children in mainland France and its departments in the Caribbean, Indian Ocean and South America.
These territories are among the youngest in France, with a high percentage of their population under 18, and among the poorest.
In the Indian Ocean department of Mayotte, eight out of ten children live in poverty, according to Unicef. In French Guiana on the coast of South America, it's six out of ten.
On the French mainland, meanwhile, poverty affects two of every ten children.
Published to coincide with World Children's Day, Unicef's report also highlights how poverty impacts children's ability to access fundamental rights, such as education and healthcare.
"Access to basic care in the overseas territories is not necessarily guaranteed," Mathilde Detrez, Unicef advocacy officer and co-author of the report, told RFI.
"Indeed the childhood mortality rate is markedly higher in these territories than it is in mainland France. In Mayotte, for instance, it's 8.9 per thousand children, while on the mainland it's around 3.7 per thousand. So the gap is considerable."
Detrez says the disparity can be partly explained by growing up in poverty, which is known to negatively affect mental and physical health well into adulthood.
But she points the finger at gaps in the healthcare system too: "It's linked to the precarity in which a lot of the population live, but also a lack of services and a lack of medical staff."