A Perth family has thanked US surfing "legend" Kelly Slater after the star saved a mother and a young toddler from "a freak wave" in Hawaii.

Father Chris White, a photographer from WA, posted his thanks to the 11-time world surf champion on Instagram after his wife Sarah and 22-month old son Van were swamped by a huge wave as they walked along a footpath close to Rockpiles - situated in front of Ehukai Beach - renowned for its surf.

Kelly Slater, fresh from his struggles at a near by competition in Waimea, was unbelievably on hand to rescue the pair after North Beach mum Sarah lost grip on Van's pram.

Speaking to Seven News Perth Sarah re-lived the terrifying ordeal.