A man stands accused of beating a Palmerston North toddler to death because the three-year-old girl got a toilet roll wet.

But defence lawyers for Sean James Donnelly, 22, say he swung three-year-old Cash McKinnon around by her legs to teach her a lesson, but never intended to drop her.

The murder trial of Donnelly began before a jury of four men and eight women in the High Court at Palmerston North this morning.

Donnelly, a security guard, is accused of killing three-year-old Cash McKinnon at a house in Hulme St in August 2009.

She was one of four children in his care when she was taken to Palmerston North Hospital with over 80 external injuries and severe internal head injuries.

She died the next day and police confirmed that her injuries were non-accidental.

In his opening statement this morning, Crown prosecutor Chris Shannon said Donnelly found a toilet roll in the toilet on the night of alleged murder.

When Cash admitted putting it there, he took her into another room to punish her. Neighbours could hear a child screaming soon after, Shannon said.

Cash was later seen by other children in the house, unresponsive, with injuries and bandages on her head, he said.

It wasn't until the next day that Donnelly contacted friends, after several unsuccessful attempts to wake Cash.

Donnelly's lawyer Lorraine Smith said her client admitted he caused the toddler's death but denied it was intentional.

He had swung her around by the ankles to teach her a lesson for being "cheeky" but became dizzy and lost his grip.

"He [Donnelly] does not know if she [Cash] hit the bed first, or how she fell...within a matter of minutes she fell over and was unconscious."

"Sean Donnelly should not have hit Cash but hitting her did not kill her. The serious injuries happened because she fell out of his hands; he never intended to let her go."

The trial is set down for three weeks.