mochi for a child's 50th day celebration
Traditional Japanese custom; mochi (rice cake) prepared for the 五十日の祝 (ikanoka no iwai), a celebration held on a baby's 50th day after birth.
See also: 五十日の祝
The 50th-day mochi is made to wish for the baby's healthy growth.
五十日の祝 refers to the celebration itself, while 五十日の餅 is the specific mochi used in that celebration.
From 五十日, an old expression read いか meaning “the fiftieth day,” and 餅, historically read もちい, “rice cake.”