An Italian grandmother has accidentally poisoned herself and three children with hot chocolate that went out of date 15 years ago.

The 77-year-old woman, named as Mrs Rosetta, reportedly found the expired sachets at home and mixed them into warm milk as a treat for her two grandchildren and their friend.

She also enjoyed some of the hot drink, along with her partner and son, Il Mattino reported.

Her partner was the first to feel the effects, suffering sickness and diarrhoea, before the whole group had to be hospitalised with food poisoning symptoms.

The family had to be taken to hospital (AFP/Getty Images)

One of the children, who were aged between eight and 12, reportedly remained in hospital for almost three weeks.

Suspicions quickly turned to the hot chocolate and when she was able to return home, Mrs Rosetta discovered that the expiry date was 5 June 1990, Il Giornale di Vicenza reported.

She had brought the drink sachets “a few years earlier” in the 1980s, the newspaper said, but forgot about them as they languished hidden in the bottom of a cupboard.

The hot chocolate’s expiry date was in the month when Italy hosted the start of the World Cup, the destruction of the Berlin Wall began, the US and Russia signed a treaty to end chemical weapon production and J.K Rowling finished writing Harry Potter and the Philosopher’s Stone.