Dylan Thomas' poem "Fern Hill" reflects on the joys of childhood. What are the negative aspects of childhood that he touches?

The poem discusses a carefree and joyful childhood, where time doesn't seem to matter, the sun shines, and life is easy. However, the last line states, "Time held me green and dying/though I sang in my chains like the sea." this last stanza discusses the fact that, though the author or speaker had a "carefree" and "heedless" childhood, time eventually runs out. The same concept of time that in stanzas one and two lets the speaker "hail and climb" and "play and be," eventually no longer allows him these freedoms. The comparison of Adam and Eve's fall from the Garden of Eden shows the boy's fall from the paradise of childhood ("before the children green and golden/followed him out of grace...). Time holds him "green and dying" as an adult, yet he still "sang in (his) chains like the sea." It is a beautiful metaphor, although he is chained by life, by only the certain amount of time that is given him, he can still sing in those chains. The knowledge and experience that comes with adulthood teaches us that time is fleeting and ignorance cannot last forever.