A boy (3) found dead as his mother pushed him on a swing was alive when she put him there two days earlier, US authorities have revealed.

Police were called when a member of the public spotted Ji'Aire Donnell-Lee's parent, Romechia Simms, pushing his lifeless body in La Plata park, South Maryland.

The Charles County Sheriff's Office said investigations revealed she had been pushing him in the swing since the pair entered the park 44 hours earlier, at around 11:15am on May 2nd.

Temperatures had fallen to 10C during the night.

Spokeswoman Diane Richardson said an autopsy found the toddler had died of dehydration and hypothermia, adding that the death had been ruled a homicide.

The county state's attorney's office will decide whether to file charges after receiving the report.

But Ms Simms is understood to have previously suffered mental breakdown, and a woman who appeared to be her mother called for understanding.

Vontasha Simms posted a picture of Ji'Aire on Facebook, and said she was setting up a charity in his honour to raise awareness of "the desperate needs of those who are mentally ill".

"There is a need that must be filled," she wrote.

"We embrace those that may have cancer, sickle cell anemia, high blood pressure, even those that may suffer from substance abuse. It does take a village to raise a child. And yes, we are our brothers' and sisters' keepers. Each and every life has meaning and a purpose."

"Those that suffer from mental illness may life a very lonely and unproductive life if they don't receive the resources, support and love that is needed."

"It could be a mother, father, sister, brother, a child, a family member or yourself. Mental illness touches every family in this country. Let's not shun them or look down upon them because it could be you."