Some entrants were from the Riversdale Surf Life Saving Club's "nipper" programme, while some competitors travelled from other parts of the district in order to take part, Mr Matthews said.
Children competed in three age divisions, with the oldest group, aged 13 to 17, completing a 75m swim, a 8km bike and a 2km run.
Children of all ages and fitness competed in the triathalon, Mr Matthews said.
"It's an opportunity for kids to get active and participate in an event that's all about fun and all about being physically active. I think all kids thrive on the opportunity to do that.
"It's an event that all kids of all abilities can participate in and give it a go ... the whole thing is about getting the kids out there, getting involved and making sure they have fun."
Next Sunday Riversdale's "nippers" will test their skills against children from across the Wellington region at the Surf Life Saving Junior Carnival, where they will compete in a variety of beach and sea events.