But in a perverse and egregious breach of trust, his drug-abusing, paranoid father Nathan Vikatos calmly took his son's life, motivated by unfounded fears.
Vikatos led Alexi into the bathroom of a Sydney apartment in May 2023, one-and-a-half hours after learning a domestic violence complaint had been made about him to police.
After neither emerged for some time, the bathroom door was unlocked with a butter knife to reveal the pair lying in a pool of blood.
The boy, who was three years and nine months old, could not be revived.
In a phone call from jail after his arrest, the killer told an acquaintance he "did himself" first and then asked his son what colour he saw.
"Red," the boy told his father.
"You want to be red too?" the father asked, before Alexi replied yes.
"Then I did it," Vikatos said.
The 48-year-old told prison staff he killed his son in an attempted murder-suicide because he wanted them to become two ghosts.
NSW Supreme Court Justice Paul McGuire said a child of such tender years as Alexi was entitled to feel safe and protected when in the presence of their father.
"By killing his own infant child, the offender has perversely and egregiously breached the trust, protection and love that Alexi deserved," he said in a decision published on Friday.
After Vikatos's arrest, he told hospital staff he knew he would be arrested but had no one to take care of his son and did not want him "bouncing around in foster care".
But he need not have felt alone, his sister told the court in a moving victim impact statement.
"She said he had support all around him in his extended family and that help was there, love was there and taking Alexi's life was never the only option," the judge said.
Alexi's biological mother Jessica Marett died of natural causes two years before the murder.
His father soon started reusing methylamphetamine.
Days before the murder Vikatos expressed delusions that police were watching him.
Unable to contact his mother, he abandoned his Blue Mountains home, taking Alexi to an apartment in Sydney.
Justice McGuire found Vikatos was experiencing bizarre beliefs spurred by paranoia that his son was better off dead than being cared for by someone else.
He had only made very limited expressions of contrition and remorse, including a guilty plea in November.
Recent claims to a forensic psychiatrist that he heard voices telling him to "kill everything he loved" at the time of the murder were inconsistent with statements made to police and hospital staff soon after, the judge noted.
Justice McGuire jailed Vikatos for 28 years and six months after a 25 per cent discount for the guilty plea.
He set the non-parole period at 18 years and six months - reducing it after finding the 48-year-old's time in custody would be more onerous because of his mental illness.
He was also likely to spend time in protective custody because of the nature of his offence.
He will be eligible for parole in December 2041.
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