The bodies of a man and two young children have been found next to a car on a bridleway.
Hampshire Police were alerted at 6.15pm on Sunday by a member of the public who discovered the bodies in Newton Stacey, Andover.
They are believed to be Michael Pedersen, 51, of Chertsey, Surrey, and Ben Pedersen, seven, and Freya Pedersen, six, both of Ashford, Middlesex, said a spokesman.
No-one else is being sought in connection with the deaths, police said.
The police spokesman said the coroner has been informed and post- mortem examinations are due to take place later.
Detective Superintendent Tony Harris said: "We are currently investigating the circumstances surrounding this terrible incident and are working to establish what has led to these tragic deaths.
"We are treating this as an isolated incident and we do not believe anyone else was involved.
"The families of Michael, Ben and Freya have been informed and specialist family liaison officers from Hampshire Constabulary, and officers from Surrey Police, are working with them to provide support and keep them updated as the investigation progresses.
"Our thoughts are with the family and friends of those involved at this extremely difficult time and I would ask that they be allowed to come to terms with what has happened in a dignified and respectful way."