To be “a child at heart” means to maintain a youthful and playful outlook on life, even as an adult. It implies retaining qualities such as curiosity, wonder, imagination, and the ability to find joy in simple things, similar to how children do. People who are described as being a child at heart often approach life with a sense of innocence, enthusiasm, and a willingness to explore new experiences and possibilities. It’s a positive way of suggesting that someone has a youthful and lighthearted spirit, regardless of their age. Liam