Tension threatened to boil over at times as he repeatedly denied acting as a lookout for the pair, or that he was privy to conversations about planning the robbery as they made their way to the dairy.
Defence lawyer David Niven said the reason the witness was not willing to talk about that conversation was because he was scared he would get into trouble.
"They hadn't even had a proper plan out ... there was hardly a plan at all," the boy replied.
He also reiterated the knife used to stab Mr Kumar was taken as a scare tactic, and that "no one was meant to get hurt."
The schoolboys on trial, who were aged 12 and 13 at the time of Kumar's death, have pleaded not guilty to the charges. Their lawyers say they lacked the "knowledge and intention" to commit the crimes.
The court proceedings have appeared to tire them at times, with the older of the two lying his head on the desk and the younger yawning through the evidence.
Meanwhile, Mr Kumar's family is expected to privately mark tomorrow's one year anniversary of his death. They have been in court throughout the trial, which is expected to last for a month.