Baby is just starting to walk but falling on knees?

I’m just wondering....my friend had a baby the same age who is also starting to walk and when she loses her balance, she falls on her butt only. Mine falls on her butt too, but she falls on her knees half the time as well. I keep thinking she’s going to cry out in pain, but she doesn’t. My friends baby is the only other one I know so I’m not sure if it’s common for a baby to fall forward on their knees? When she’s just getting up to stand, she’ll brace herself with her hands, but only then.