Booker had represented New Zealand at an Australian national championship, but never at a worldwide competition.
"I'm pretty stoked and excited, but it's going to mean a lot of fundraising. My goal would be to make semifinals.
"There will most likely be training camps [with the New Zealand team]. We will have training programmes to do throughout the year as well, so by the time we get to worlds we'll be at our peak strength."
Gardner said he competed at the event in Austria last year and enjoyed it.
"I learnt you need to train really hard to do well. This year I'd like to finish in the top 50 per cent. I need to practise on the walls over there because they'll be different to here."
He will compete in bouldering, lead and speed climbing and said bouldering was his favourite.
"It's more about strength and technique. I actually got into climbing through Henry about five years ago, he told me to come and have a go. I didn't really like team sports when I was younger, there is more pressure but if you fall or whatever you don't have others who are disappointed. You also don't have anyone to push you, though, so you have to be motivated."
The boys' coach Max Warren said it was "awesome" they had been selected.
"I'm very proud of them, I've seen them grow in the last few years and they have come a long way."
Warren said it took talent, discipline and dedication to get ahead in climbing.
"In a team sport you can rely on other people, with climbing it's either you do it or you don't. You see these boys in here every day after school, they climb and they have their plans, strength training and endurance training.
"In terms of rock climbing, New Zealand is very small, the United States and Europe are really strong, but if these boys train really hard up to the competition who knows what could happen.
"Climbing is good for young people because there is adventure in it, it's a more adventurous sport and it gives you a thrill. You set yourself a goal, you have to get to the top, whenever you reach that goal you are proud of yourself."