The song 'You're Just A Baby' by Belle & Sebastian delves into themes of innocence, growth, and the passage of time. It explores the journey from childhood to adulthood, capturing the essence of youthful naivety and the inevitable transition to maturity. The lyrics paint a picture of someone coming to terms with their place in the world, grappling with the expectations and responsibilities that come with growing up. Key poignant moments in the song include reflections on the simplicity of childhood and the contrasting complexity of adult life, emphasizing the bittersweet nature of this progression.