The heartbroken father of a boy murdered by his mum on the Yorke Peninsula has told 7 News he was locked in a bitter custody battle.

He claimed he had raised serious concerns about the boy's welfare to authorities but says it fell on deaf ears.

View photos 'We've got some bad news for you': Jacob was killed by his mother before she took her own life. Photo: 7 News More

When police officers knocked on Mick Clarke's door yesterday, his heart sank.

Seven-year-old Jacob died at the hands of his mother Tanyia Hewson, who then took her own life.

"They've gone, 'we've got some bad news for you, we found your ex-partner and your son deceased'", he said.

Tanyia's husband made the discovery at their home at Tiddy Widdy Beach.

View photos Heartbroken father Mick Clarke said he was devastated to hear of Jacob's death. Photo: 7 News More

View photos The Tiddy Widdy Beach home where the tragedy occurred. Photo: 7 News More

"I'll never get to watch him graduate school or go and play sport or do anything," Mr Clarke said.

A devastated Mr Clarke said he'd been fighting for custody for years.

"She was an unstable person, but I could never have imagined her killing him," he said.

He alleges that his concerns he raised with authorities went unanswered.

"It just went in one ear and out the other," Mr Clarke said.

"No-one really listened to what I had to say and this is the outcome."

The child protection department says the family was known to them but that no alarm bells had been sounded in the past two years.

View photos 'Rest in peace, my special little man'. Photo: 7 News More

Police had been sent to the property a number of times to do welfare checks on the family.

Police say that will form a part of their report.

"I love my boy to bits, I'm actually going to go and get a portrait of him on my chest tomorrow," Mr Clarke said.

"Rest in peace, my special little man."

If you or someone you know is struggling mentally contact Lifeline for support on 131114.