According to a report in The Sun, the girl aged 12 years and three months gave birth to a seven pound baby girl last weekend.
The girl became pregnant while still at primary school soon after she got into a relationship with a boy who lives near her house in north London, the report said.
The proud parents posted a picture of them posing with their baby daughter online.
The young mother, who lives with her mother, hopes to return to school in September.
At 27, her mother is one of the UK's youngest ever grandmothers.
The grandparents on both sides are shocked but supportive and want the two to stick together and bring up the baby.