Smith won both the 100m and 200m breaststroke with times of 1:09.76 and 2:29.30 respectively, while also coming third in the 50m (33.00).
He also gained personal bests in the 200m medley (2:21.18) and the 400m medley (4:57.90).
O'Keeffe set both open and age grade Wanganui records in the 100m and 200m freestyle.
Her 2:10.00 time in the 200m earned her third place, while she was placed 5th in the 100m in 1:00.78.
O'Keeffe also placed third with a personal best 1:07.42 in the 100m backstroke, and had solid performances in the 200m and 400m medley, along with the 100m and 200m butterfly.
"Also at the Wellington Champs Elena Forlong, 14, had an outstanding 800m freestyle in a closely fought race with Ruby Heath from Wellington," said Lowe.
"Forlong set a new Wanganui age and open record of 9:33.10, improving 19 seconds on her previous best."
Another 15-year-old, Sophie Couper, placed 5th in the 200m backstroke with a personal best of 2:26.18.
These swimmers will be in action at the Wanganui Spring Meet on September 14-15, with a team of 10 heading to the New Zealand Short Course Champs in Wellington from September 29.