In episode four, two year-old Jefferie Hill went outside to play, saying, "I won't go away, Mummy." So how does mum Jo Reynolds and his family deal with the fact they've never seen him again? What happened to him?

Watch a video segment from the episode here

Jefferie Hill would be 52 years old today - but when his mother last saw him he was just a toddler.

Jefferie disappeared on September 28th, 1968; Keith Holyoake was still Prime Minister of New Zealand. The 2-year-old had been playing in the neighbour's back yard before heading towards the Matarawa Creek in Tokoroa.

It was thought he fell in the water, but despite the creek being drained and an extensive search carried out for days and weeks after he disappeared, Jefferie wasn't found. Doubt has crept in and other scenarios investigated, yet there have been no answers for a family that has never forgotten their precious boy.

Jefferie's mother, Jo Reynolds, and sister, Laura Hill, told RNZ's podcast, The Lost, they've had their doubts about Jefferie falling in the rubbish-filled water.

"There is no way in the world he would have got through that rubbish," Reynolds says. "That's why I wonder whether he's been picked up. He's been taken."

The creek is about 3m wide and 1.5m deep, and was used as the neighbourhood dumping site. Jefferie went missing on a Saturday morning - the first beautiful day of Spring after three weeks of rain.

He went outside to play with the neighbour's little girl, Karen Stubbs, about 9.30am. Jo kept an eye out for her son through a window, and last saw him tipping a bucket over his head in a sandpit.

"The next thing I heard Robert, my oldest son who was six at the time. I heard him scream and I knew he'd been riding his little bike," she says.

"I thought 'oh my God, he's put his foot through the spokes' and it was the neighbour, the mother of the little girl, coming over to tell me that Jefferie had gone into the creek."

The last person to see Jefferie alive was Karen Stubbs. She was only two years and nine months old. Hundreds searched for Jefferie. A red plastic spade belonging to him was found nearby.

The creek was drained and rubbish removed. Residents looked under buildings and houses. But Jefferie wasn't found.

Former Senior Sergeant Ronald Moncur, 84, was part of the search, and now lives in Auckland.

"It was a quite populated area. You would have thought he would have surfaced somewhere along the line," he says. "I don't know what else I could do and I still don't know what I would do if it happened again. We did our very best to find him."…

Go to this episode on rnz.co.nz for more details