When I was a younger player I was constantly in knee pain. My father had terrible knees but was overweight so I attributed his knee issues to that but I also knew that part of it was genetics and that I was going to have to deal with it as well.
When I was 13 years old it got so bad that I couldn't play more than a couple hours a day because of how bad my knees would hurt when I would go up or down stairs. The pain was even worse when someone hit my knee straight on or when I fell to the court on it.
After a year of knee pain I told my dad I needed to go to the doctor to get it checked out. What we found out was that I had a disease or syndrome called osgood schlatters. These were bumps that formed at the top of my tibia right below my kneecap. They are ruptures of a growth plate in that area and they affect a ton of kids around the ages of 10-16 who are engaged in sports.
You may be reading this now wondering if you have them and if you do you would know it. You'll have extremely painful hard lumps that look like they are all bone and when you hit them you are in great pain. They are very common and have no cure except to stop growing or to stop playing sports altogether. In fact, I had several friends who didn't play basketball for a summer because they hurt too badly.
To treat them during games I made sure that when I came out of the game I couldn't sit down. I would stand up or if I sat I would make sure that I kept bending my knees. By sitting they would simply freeze up and be nearly impossible to get warmed up again.
Another common injury among young players is the dreaded high ankle sprain. The first sprained ankle is always the worst one. It's the ligaments really being stretched like they never have before and is usually the toughest one to recover from.
High ankle sprains will create swelling all over the outside of the ankle and you'll notice color around the outside bone but mainly down by the heal. Ice this injury and don't push it. These injuries can be tough to recover from.
You will see pro players miss a month with a serious ankle sprain so it isn't uncommon for it to be the same timeframe with youth. However younger players have been known to heal quicker due to the fact that they are still growing and have more stretch in their ligaments but I don't think that has ever been proven.
The other most common injury is simple tendinitis. Tendinitis is irritation of the tendon but players can get tendinitis in their elbows, wrists, knees or ankles really and it is common in young basketball players who play a lot. You'll feel very sore when not playing and even while playing you'll notice some soreness of the affected area.
Tendinitis is treated with ice and rest. It's an irritated and overworked tendon so it is critical to get proper rest and to treat your body the right way. Players usually try to play through tendinitis though and it can be quite painful. Most of the time players will get warmed up and be able to go just fine but afterwards will feel very sore. It only makes the postgame or post practice rituals more important.