Are babies really born without knee caps? No not really, but they don't start out with the knee caps we know as adults. Baby kneecaps are made of cartilage and develop into bone through ossification. Baby knee caps don't even show up on x-rays, they are very soft, flexible and actually pretty darn durable. With all of the crawling and the toddling that includes endlessly bumping them, baby's knees really are like pint size heavy duty shock absorbers. Ossification (cartilage hardening to bone) starts at about 3 years of age and continues until about age 6. What perfect timing for the process of ossification to start after the rugged, rough and tumble months of learning to crawl, stand and walk.