But human babies keep on gaining fat too. Infant fatness peaks between 4 and 9 months of age at about 25 percent before it begins a long slow decline.

Why do babies get chubby?

Babies are meant to gain quickly

Babies store some of that fat under their skin because their developing bodies and brain need quick hits of energy all the time. Your baby might have some body rolls or big, soft cheeks. Don't worry — this kind of “fat” is normal and healthy for your baby.

When do babies lose chubby cheeks?

Chubby cheeks, chubby hands, chubby belly: They make babies so huggable. But that pudgy appeal can quickly become a health concern. “It's normal for a child to slim down between ages 2 and 5,” says pediatrician Roy Kim, MD. “Your child will look their thinnest about the time they start kindergarten.”