first line of a children's cold-weather rhyme
A set phrase from a traditional nursery rhyme, comparable to the English 'It's Raining, It's Pouring'. Used by children on cold days, often while rubbing hands together.
On a cold day, the children were singing 'Ōsamu Kosamu' while rubbing their hands together.
The phrase comes from a traditional Japanese nursery rhyme. 大寒 (great cold) and 小寒 (lesser cold) refer to the coldest periods of the year, and the rhyme is associated with children's play in winter.