It means that people with daughters will send flowers and cakes to their mothers in leap months, March and April. Folk call it "mother cake", which means that I hope my mother will live a long and healthy life and stay with my daughter forever, which means health and longevity.
"In the leap month year, stay in the mother year." There has been a folk saying since ancient times that leap month has been harmful to mother's health since ancient times. "Mother-in-law cake", also known as "leap moon cake", is not good for mother's health for more than one month in a year. It refers to the flower cakes made by children to please their mothers.