Research by the Children's Society and Hampshire social services identified 91 children between the ages of three and 17 in the Winchester area as young carers.
It revealed schools in the county did not know any children who were caring for sick relatives on a long-term basis or assuming parental responsibilities for younger siblings because their parents could not do so. Only one primary school had made a referral to the project team.
"It was apparent throughout the whole of the study that some schools did not regard young carers as their concern," said its report, Couldn't Care Less.
The report said it took several months for staff to realise that caring for a sick relative affected children's learning.