"Our global issues committee is one of the biggest in the school and, for others it might sound stressful, but I think for both of us it's an opportunity to get girls to help wherever they can - whether it's in our community or worldwide," Smith added.
Those who take part in the 40 Hour Famine, which starts on June 5, can choose their challenge or select something to give up – like going without transport, furniture or technology – and ask people to support their efforts by donating.
Both girls have taken part in the famine before. Brock has done it for the past three years, giving up technology the first year and food the last two years.
Meanwhile, Smith participated once before, in 2017, doing the backpack challenge where you live off limited supplies in a backpack - canned food, water and clothes.
This year the girls were still deciding whether they would do the backpack challenge, or go without furniture for 40 hours.
"Basically the no furniture one is you can't use any chairs, you can't use your bed - you have to sleep on the ground. If you're eating at the table, you have to stand and eat.
"It gives you the perspective of kids around the world who don't have that luxury ... I think that's something that will challenge us," Smith said.
For more information on the 40 Hour Famine, including how to donate, visit www.worldvision.org.nz/40-hour-famine