In the latest in a history of under-age pregnancies in coastal town of Poole, the boy's 14-year-old girlfriend is several months pregnant, the Daily Mail reported.
The two children, who cannot be identified for legal reasons, attend the same school.
In the case, the local authorities have obtained a court order to stop the identification of the two children.
Earlier this year, Alfie Patten, 13, from Eastbourne in East Sussex, was believed to have become a father after 15-year-old Chantelle Stedman conceived.
But DNA tests later showed that another 15-year-old was the father.
In 1997, Jenny Teague became the country's youngest mother at the age of 12. Two years later, sisters Charlene, 17, and Miranda Way, 15, from Poole town gave birth within months of each other.
Sean Stewart became UK's youngest known father when, in 1998, at the age of just 12, his nextdoor neighbour Emma Webster, 15, gave birth to their baby.
Pregnancies among girls under 16, below the age of consent, are at their highest in the country since 1998.
The UK Government has attempted to cut teenage pregnancies by handing out free contraceptives and expanding sex education.