Running is a Great exercise to damage your knees.
Most children happily run around all day and rarely develop any issues. Adults have an unfortunate habit of becoming quite sedentary, losing any conditioning they had and then going out and running distances their body isn't prepared for. Then people will blame their shoes or even the activity itself when the most significant factor is doing too much too soon.
This interview with Daniel Lieberman[1], an evolutionary biologist out of Harvard, is a good read about the misconceptions associated with human activity and what studies of our historical behaviour can tell us about what is and isn't important in staying active.
https://news.harvard.edu/gazette/story/2021/01/daniel-lieber...
I am an adult and I definitely have kept issues from things that I did as a child.
Now, seriously, isn't the body weight to joint surface ratio completely different for children and adults?
What can be done to fix such injuries?
Prevention is key for these-- particularly by familiarizing your body with the loads incrementally. While some may have the aerobic fitness to complete a 5k (even if they're new to running-- a cyclist or swimmer, perhaps) the musculo-skeletal adaptations involved with consistency haven't occurred yet, and injury is a lot more likely. Even elite runners, when they're "getting back into it" start with alternating run-walks to avoid the "too much, too fast" loading.
Most of these can be addressed by seeing a physiotherapist, and normally involve cutting mileage or pace significantly and/or strengthening weak supporting muscles.