Chaochao was indeed a difficult baby to care for, always crying and whimpering. Throughout the entire full moon celebration, except for the times he was hungry and was held by Ye Wanwan for a while, Shen Yi had been holding Chaochao the rest of the time.
Yet Shen Yi didn't feel burdened at all, and was even honored and a bit proud of himself for being able to soothe Chaochao.
Whenever Zhouzhou was at home, he took care to be by Chaochao's side every moment, not at all annoyed by his sister's frequent crying.
Moreover, Zhouzhou had learned from his best friend that small babies who can't speak yet only cry to indicate they are hungry or uncomfortable somewhere.
As a result, whenever Zhouzhou heard his sister crying, he worried whether Chaochao was hungry or perhaps uncomfortable.
In the beginning, Ye Wanwan also had such worries, but after observing, she realized this was not the case; the most likely explanation was simply that Chaochao was a crybaby.