These things—
Is a memory that will never die:
In the garden under the moonlight,
Under the leaves of vines,
Mother's lap.
The dash here means that the following words are specific explanations of "these things".
Childhood memories such as "Moonlight Garden", "Under the Rattan Leaves" and "Mother's Knee" are all manifestations of mother's love, and they all have her voice and face. These scenes can make us feel her kindness.
The poem does not directly describe the image of the mother, but expresses the author's nostalgia and memory of childhood life, as well as his deep yearning for his mother and praise for his maternal love by recalling the childlike things that happened in "Moonlight Garden", "Under the rattan leaves" and "Mother's lap".