What does the poet miss about his childhood days?

Watching the little butterfly poised delicately on a yellow flower for half an hour stirs happy childhood memories for the speaker. He remembers those "sweet childish days" when he and his sister Emmeline would chase butterflies around the little plot of orchard-ground. For the speaker, this was almost like a hunting expedition, but his sister was so sweet and so gentle that she feared to brush the dust off the butterfly's wings.
The butterfly's lack of movement indicates a certain reticence on its part. The speaker urges the shy little creature to fly away from the yellow flower and rest his weary wings among the trees of the orchard, where the speaker and his sister will reminisce about their idyllic childhood full of sunshine and song.