Chris Sims starred for Didcot Barramundi in the Oxon and North Bucks County Championships at Aylesbury, taking three golds back to south Oxfordshire.
The 12-year-old won nine medals overall, setting new club records as he won the 50m, 100m and 200m breaststroke events.
His older brother Nick Sims, 14, won eight medals, including silver in the 200m breaststroke.
Team mate Ben Newell, 12, also took home nine finalists medals.
Newcomer Ben Titchener, 13, gained silver for 100m freestyle and bronze for 50m butterfly among his five-medal haul.
Sisters Isabelle and Maddison Langley shone in the backstroke and freestyle events.
Maddison, ten, making her counties debut, won seven finalists medals, including a bronze in 100m backstroke.
Big sister Isabelle, 12, gained two finalists medals and a regional time for 100m backstroke.
Another sibling pair, Alexander, 14, and Eliza Nicholson, 11, won medals for 50m freestyle, 50m backstroke, 100m backstroke and for 50m, 100m, 200m breaststroke, respectively.
Lauren Kernan, 15, claimed silver for 50m freestyle.
She also came third in the junior championship for this event.
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