Their dearest songs implies this occassion is usually enjoyed by the group and they look forward to it regularly
The caddles mooning in their face in the poem this can be interpretted to mean that it was winter, or December season when many people celebrate various occassions.
Brightest things might mean a sense of value as well as some memory shining in the mind.
Throngs has something of the sound of dry leaves being brushed together, or falling against one another.
Ploughs in this poem implies agricultural activity of preparing land for new life and the act of memory brings those long-gone moments back again.
Summary of interpretation
In During the wind Thomas has used various techniques. In the first few lines of each stanza, refers to times of bright times in life. He uses outdoor activities to during spring and summer to show this. In the last lines of each stanza he uses the colder seasons fall and winter to show how human condition can change from happiness to sadness. In reality this takes a number of years but eventually there is nothing human can do to stop these inevitability events.