In "The Echoing Green," Blake describes a group of children playing joyously and carefree on the eponymous green. The adults watch the children playing and remark, "Such, such were the joys." This quote links to a key Romantic idea that childhood is a joyous and carefree time which, unfortunately, does not last for long. The adults are indeed nostalgic about their old childhoods.
In "The Chimney-Sweeper," Blake highlights and criticizes the use of children as chimney-sweeps. In London in the eighteenth century, children as young as five years of age were made to clean chimneys. The work was dangerous and often fatal. In the poem Blake, imagines a dream that one of these children might have. In the dream there, are "thousands of sweepers … locked up in coffins of black." This quote clearly emphasizes the fact that these children were being sent to their deaths, and that, by implication, the society that allowed this was complicit in child abuse. Highlighting the importance of childhood, and also the maltreatment of children, was a key characteristic of Romantic poetry.
In "Laughing Song," Blake celebrates the beauty and joy of the natural world. The joy of nature is captured in the opening two lines:
When the green woods laugh with the voice of joy,
And the dimpling stream runs laughing by.
Nature, in the form of the woods and the stream, is personified in these lines. The "laughing" and the "voice of joy" suggest that the joy of nature is audible and irrepressible. Throughout the poem, to suggest just how irrepressible is the joy of the natural world, Blake describes the hill, meadows, grasshopper and birds all laughing in unison. The joy of nature is also of course a key characteristic of Romantic poetry.