Kate Fox, a close friend of all three involved, said police were called to the handover point at Neutral Bay, on Sydney's north shore, after Ewing initially refused to give up custody of his son, Daily Mail reports.
Fox said, "Dan was dropping Archie off and Dave instead of Marni, because she wasn't feeling well."
It's understood that Ewing refused to handover his son to Mr Robertshaw as Ms Little was not present.
After an alleged dispute that lasted close to an hour, an "altercation occurred" between the child's father and step-father, the Daily Mail reports.
Police were allegedly called to the handover point, at which time the dispute was resolved.
Ewing and Little split in December 2015.
The alleged incident came just days before Ms Little and Mr Robertshaw's wedding.
Tying the knot in an intimate ceremony, Little told New Idea: "I've been Marni Ewing for so long now and just didn't want that identity anymore."
"Dave is so wonderful with Archie and loves him like his own, so it was only a matter of time before he popped the question."
