The two big kids pulled on the boxing gloves, doing pad-work mostly in their Campsie backyard, but inevitably shaping up for a spar.
Boom. The 15-year-old, Mike, lands a thumping hook on brother Allan, whose 12-year-old frame drops to the floor.
"That was the last time I tried to fight him," Allan says.
Ten years later, brothers Michael and Allan Alaalatoa are shaping up against each other once more; poised to become the first siblings to play each other for Super Rugby teams from different sides of the Tasman.
They're Sydney-born and raised but rugby and circumstance have taken props Allan to Canberra and Michael to Christchurch.
Sydney's Alaalatoa clan, led by father Vili - the former Samoan international - will travel down the freeway on Sunday to watch 125kg Allan pack down for the Brumbies - Australia's most successful franchise - against 136kg Michael's Crusaders - the competition's most successful franchise, in Canberra.
The Brumbies were quick to spot Allan's potential and signed him three years ago before the Waratahs had a chance. Michael, who was training at the ARU's national academy in Sydney alongside his younger brother at the time, was bought into the Tahs system but was left to play club ruby for West Harbour before his sole Super Rugby appearance at the start of 2014, the year NSW won the premiership.
Last year, after failing to get another opportunity, Michael was told by NSW his contract would not be renewed and his future looked grim.
"It was a tough period, my lowest point, I needed a change," Michael says.
"I wanted to get out of Australia and play somewhere else for enjoyment, because I'd lost my love for the game."
So he went across the ditch to play in New Zealand's domestic ITM Cup on a three-month contract for Manawatu.
Few could have forecast that Mike would have produced the form that not only saw him contracted by the Crusaders but also come off the bench to play every game so far in 2016 - except Allan.
"He got released by the Waratahs, didn't have anywhere to go, but I've always backed my brother and it has worked out for the best," Allan says.
Mike, a tighthead, is learning under the tutelage of All Blacks Joe Moody, Owen Franks and Wyatt Crockett.
Allan grew up playing as a tighthead, playing three years straight for the Australian under-20s side, but injury at the Brumbies led him to switch to loosehead, where he now supports Wallaby No. 1 Scott Sio.
He's performed so well that Wallabies coach Michael Cheika brought Allan into the national camp at Cockatoo Island a fortnight ago.
"I'll catch up with Mike before the game, we'll have dinner, but when we cross that white line we'll be enemies," Allan says.
"Then afterwards he'll probably crash at my place and we'll have a laugh about it."
Mike adds: "It's not such a big deal playing against each in general play because you hardly get the chance to put a big one-on-one shot, but scrumming is different.
"When you're scrumming, it's very personal, macho.
"You don't want your ego to be dented, especially when you're going up against your brother."