It's hard to keep a secret when you're a member of the royal family, but somehow Kate Middleton managed to do just that.

Despite being in her third trimester, the Duchess of Cambridge has been making several public appearances with a genuine smile plastered on her face.

This Tuesday, Middleton and her husband, Prince William, visited an outdoor ice-skating rink in the center of Stockholm, Sweden to play a game of bandy hockey and meet the local schoolchildren.

But that wasn't the first time she's met kids this year. On January 22, Middleton went to an elementary school in London to talk about the importance of taking care of your mental health.

"I see time and time again that there is so much to be gained from talking of mental health and taking the mental health of our children as seriously as we do their physical health," Middleton said. "When we intervene early in life, we help avoid problems that are much more challenging to address in adulthood."

While the royal makes time in her busy schedule to bring awareness to causes close to her heart, she doesn't always put her good deeds on display.

When Middleton got her hair cut at Kensington Palace last summer, she reportedly suggested to her stylist that instead of just discarding the tresses, they donate them to a charity that makes wigs for children suffering from cancer.

She ended up secretly donating seven inches of her luscious locks to the Little Princess Trust. The organization makes wigs from real hair and donates them to children who've lost their own from hair from chemotherapy and radiation treatments.  

"It's lovely to think that somebody, somewhere "” probably more than one person "” has received a wig containing Princess Kate's hair," Helen Creese, a spokesperson for the charity, told PEOPLE.

"It's a really lovely thought and it's fantastic for raising awareness, plus it's gorgeous hair "” we all lust after that hair!" she added.

The Little Princess Trust was created 12 years ago by the parents of Hannah Tarplee, a five-year-old girl who passed away from a cancerous tumor.

The charity has since donated more than 5,500 wigs to sick children. It can take anywhere from seven to 10 hair donations to make a single wig.

Have you ever donated your hair to charity?