Dame Deborah James shared some heartfelt advice in a letter for her children before her death.
The cancer campaigner and podcast host died in June aged 4, six years after being diagnosed with bowel cancer.
Following her diagnosis, she shared her life lessons in a new book, How To Live When You Could Be Dead, which is set for release on 18 August.
In an extract published by The Sun, James told her children – Hugo, 14, and Eloise, 12 – to “be brave”, “take chances” and “be your number one cheerleader”.
James said the “hardest lesson of all” is learning to balance “living in the now and being present in the moment with your plans for the future”.
She also encouraged them to buy a dog, noting that her cavapoo Winston made her “so happy”.
“Nature and animals make me happy,” she said. “It is only towards the end of my life that I have really started to appreciate nature.”
She urged Eloise and Hugo to find happiness in the small things, writing: “Each day, do things that make you happy – build them into your life and never criticise others for the things that make them happy.”
James also reflected on her marriage to husband Sebastien Bowen, whom she described as the “love of my life”.
Sharing what she had learned from her own relationship, James told her children to “marry only for love”.
“I wish I had learned at a young age that making time for your marriage to work should be as much a part of your timetable as going to the gym or cleaning your teeth,” she said.
“It’s important that you don’t allow the big arguments to build up, when all you really want is to forget about everything and cuddle the one person who you love.”
Following her diagnosis with stage 4 cancer, James devoted much of her life to raising awareness of the disease.
In May, she announced that she had moved to hospice-at-home care because her body was no longer responding to treatment.
At the time, she launched the Bowelbabe Fund to raise money for Cancer Research. Donations to the fund have since surpassed £7m.
One of James’ key messages to her children was to appreciate “each and every one” second of their lives.
“We are given 86,400 seconds every day, and we each choose how to use them,” she wrote. “It is only as they begin to slip away from us that we understand the value of each and every one of those seconds.
“So, my greatest advice to you is that you can do whatever you want with those seconds. You can use them however you want.”