Head judge Mike Jensen said Mr Khoo's design changes culture, engaging children's creativity and encouraging families to get involved in more outdoor play.
"In a current environment, where we have so much digital distraction, this is a welcome break for parents and kids ... the prototype is well resolved," Mr Jensen said.
"Tree Mount shows a strong understanding of aesthetic design."
Mr Khoo won $5200 from the James Dyson Foundation, a prize pack from the Intellectual Property Office of New Zealand and a year's membership of The Designer's Institute.
Mr Leyton's one-size-fits-all bike helmet uses a tension system so wearers can adjust the shape of it to their head.
Miss Warren said she sought to create a long-lasting shoe made only of natural materials from New Zealand, while reviving the craft of shoe-making.
Her design didn't require any glue, instead using the adhesive nature of wool felt to attach the shoe's elements.