Your Baby Is Born With Knee Caps. All of us do.

Babies are born with kneecaps made entirely of cartilage, so their knees are called cartilage patellae (literally cartilage kneecaps). It's simply that their kneecaps are made of different material than older children's and adult's kneecaps, it's not that they don't have knee caps. The kneecap will start to form bone at multiple centers within the cartilage. About 5 percent of the time, some of these bone centers do not fuse together with the main bone center. These cartilaginous kneecaps will eventually harden into the bony kneecaps that we have as adults.