The speaker looks back at childhood and wishes they could return to it. Back then, the worst pain was a scraped knee from a fall. Now the worries are quieter and heavier: counting the calories in a slice of toast, or lying in bed comparing themselves to other people. The poem sets these two stages of life side by side, and the contrast does most of the work.
What stands out is how small and ordinary the adult worries are. Nobody in the poem faces a dramatic crisis. Instead, the speaker is worn down by constant self-monitoring and by caring what others think, something they remember not doing as a child. The mood is wistful and tired, with a note of real desperation in the last line, "please oh please take me back." The plain wording and lack of capital letters make it feel like a private thought typed out late at night, honest and unpolished, which suits a speaker who just wants to feel carefree again.