The Herald Sun said more than 15 people closely connected to the Mach family turned out to watch the brief hearing, including the boy's stunned mother who sat holding a small teddy bear.
Many sat wiping away tears even before Cai was marched in flanked by security guards.
Family friend Diana Teoh, who had known Alastair since birth, told the newspaper he was "very bubbly, a very good boy".
"They (Alistair's parents) are trying to be strong for the rest of the family but they are definitely very devastated," she said.
"We don't know what to tell our children too because they played with him all the time."
Cai will return to court for a committal hearing on July 22.