A mother killed herself and her five-year-old son after his father was awarded custody, an inquest heard.
The bodies of Cheryl and Leo Tompsett, from Maidstone, were found at the Beachy Head cliffs in East Sussex on 18 June.
The 42-year-old bereavement councillor left a note saying she did not want anyone to “have” Leo if she could not.
East Sussex Coroner Alan Craze concluded her death was suicide and her son was unlawfully killed.
Hastings Coroner’s Court heard Ms Tompsett had been treated for depression for years and her mental health had worsened.
Her death came after a court ruled Leo should be looked after by his father, Mark Woodhams.
The coroner said Ms Tompsett had written a note to her former partner saying she did not want anyone else to “have” Leo.
Mr Woodhams said: “Cheryl had started to behave erratically but more recently there was a noticeable change in her behaviour.
“This had given us all concerns about her own mental health.
“I didn’t believe she was able to care for Leo at present.”
The night before their deaths, Ms Tompsett took Leo out for dinner with friends but never returned.
Mr Woodhams alerted police and the two bodies were found during a search the following morning.
Mr Craze said: “I’m in no doubt whatsoever that tragically Cheryl came to take her own life.
“This poor lady suffered seriously from mental ill health.
“Having read the letter addressed to you [Mr Woodhams], there is no space for 1% of doubt about what happened to poor Leo.”