The halfback posted his support for school friend Megan Hennessy's 2-year-old daughter, who was recently diagnosed with cancer.
"I went to Feilding High School with Megan and to hear her daughter Paige has been diagnosed with an aggressive brain tumour really hits home — especially since becoming a father," Smith said on Instagram.
Smith and the rest of the squad signed a 2019 World Cup All Blacks jersey to raise support for Paige and her family. The TradeMe jersey sale closes next Thursday.
Paige has a rare form of the disease. In the past few weeks she has had four operations, and is having chemotherapy.
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Hennessy said that Paige would have another MRI in two weeks when they would decide on her further treatment.
Hennessy and her husband Chris have stopped working to spend their time with Paige. Their other daughter, Caitlin, who is 4, also spends a lot of time with her sister. Hennessy said the girls had "the most beautiful relationship."
"The nurses often say that Caitlin is the best medicine for Paige."
She said the family had been overwhelmed by the fundraising support.
"We are so thankful for what Aaron and the All Blacks have done for us ... we both played number 9 in high school rugby and I remember him yelling at me on the side of the field giving me tips.
"People have blown us away with their kindness and generosity... our little town has really rallied together to help us."
The family had spent most of their time in Starship over the past few weeks, staying at Ronald McDonald house last week.
A Givealittle page had also been set up by family friend Anne Tahaafe, raising $57,070 in just four weeks.
"Thank you from the bottom of our hearts. We see every message and every donation. Through this really horrible time it's been able to keep our family together."