Sakura-mochi consists of half-pounded sticky rice dyed pale pink and a salted chelly leaf. Azuki bean paste is stuffed inside. You can eat the leaf, but there are people who don't eat it. I eat the leaf because salt makes the sweet tastier.
Uguisu-mochi is made of rice cake and azuki bean paste. Soy bean powder is sprinkled around.
Both cherry and Japanese nigthingale are representative things that indicate Spring. According to the lunar calender, February 3 or 4 is the first day of Spring. People expect Spring's coming seeing those sweet sold at stores.