Jamil 'JB' Baskerville Jr was present when his mum's partner, Zachary Tricoche, 24, started arguing with her about her food purchases, a court heard.
The two-year-old became upset and 'stepped in to intervene' after Tricoche allegedly shoved the woman at a home in New Jersey, US.
This enraged Tricoche, who punched the 29lb youngster so hard in the chest that he fell onto a wall and struck his head, prosecutors said.
When JB got back up, the boyfriend then allegedly told the tot to 'put up his hands' to fight like a grown man before punching him a second time.
The impact of the strike caused the child to hit his head against the wall again, and left him with severe injuries to his organs, NBC reports.
He tragically bled to death after his tiny liver was crushed, a medical examiner ruled.
Now, Tricoche, from Pennsauken, has been arraigned on first-degree murder charges following JB's death on the night of August 20.
He did not enter a plea and his bail was set at $1million cash, according to Fox 5 .