To be a kid at heart means to have an innate curiosity for life. Always asking questions, always wanting to know more.
Kids can be strikingly resilient, adapting to new environments remarkably quickly. At this stage of development, the brain is wired to learn and gain new skills a bit quicker than adults.
Being able to harness that power you had as a kid now, as an adult, can improve your willingness to learn, try new things, and maintain a positive outlook on life.