First book

The first book in a Harry Potter series is "Harry Potter and the philosopher stone". Main characters there are still kids so there are not that many injuries in the book. However three people eventually were hurt there. 
We will look closer on each case as the story goes.
First person, who was injured, appeared to be Neville Longbottom. And as the story goes we will know that that’s not really an unusual accident as Neville is known for his clumsy behaviour. Even though it is not his main feature it is rather important to know for the story that he is in some way prepared for such things as he aware of his own ponderousness.
This happened during the first quidditch lesson at Hogwarts. Madam Hooch – their teacher gave clear instructions on the first move that they were supposed to learn – sit on the broom and fly a few meters up the ground. However Longbottom successfully failing the first task lost the control of his broom and fall down on the ground. 
To understand the whole seriousness of situation we need to know how high he was in the air as there was no other factors affecting him accept from gravity we can predict the injuries. Professor said “few feet above the ground” where few means “more than one” or “more than three” as they are eleven years old kids we can count that they were supposed to fly around 2 or 1 meters up as 1 feet equals to 0,3048 meter. Than we include the words about the lost control and assume that he might have flew up a bit higher which I would make the highest of three meters as he slipped to the ground pretty fast and the process of flying up is rather smooth. 
Thus we would consider that he fell from the height of 3 meters. A person could not be heart severely when falling off that height even when it’s not jump. Neville was sitting on the broom so he was falling not on his legs one hundred present. The most in danger part was neck, spine and hands. But you are not supposed to broke your neck while falling prom that high on the ground so the worst thing that might have happen to him and eventually happened - he got his wrist broken. 
In conclusion, I might say that this injury in pretty accurate to real life even though we cannot really check it directly due to lack of magic artefacts in especially my property unfortunately. Also, if somebody owns any types of broomsticks, or other artefacts, or plants, or animals that would be mentioned in this article you may send them to me to make this work even more accurate. I will check them all and tell my readers the whole truce about accuracy of real life experience in Harry Potter books.
Second person, who was injured was Ron Weasley.  Strangely enough in this book Harry won’t be on the list. He fainted once but that was a curse, so we won’t count that. Back to Ron – during their operation for saving Philosopher’s Stone from Snape he was knocked out by a stone queen of chess. “She struck Ron hard around the head with her stone arm and he crashed to the floor. He looked as if he’d been knocked out.” So according to the explanation we can probably say that he was hit by a rock that fall on his head with some power. 
We will equate this situation to when a kid would be hit with a rock that somebody has thrown at them. So first step is to understand the size of the rock. As the chess were described as “all taller than they (kids) were and carved from what looked like black stone” we may say that the size of queen’s arm might be 1.5 times bigger than child’s arm probably like an average adult’s size and so would weight 13,5 kg if we would assume that the stone that they saw was black granite (average human weight is around 70 kg one arm is around 6,5% of the body weight which would be around 4,5 kg; the density of human body is around 1000 kg/m3; the density of the black granite is 3000 kg/m3). Considering this as the most probable truth we will move to the next point of hitting Ron. It is said that he was “struck hard” so at least at the speed of freefall which is 9,81 m/s2 so the power of the hit was 132.435 kg/m2*s2 which is not much at all it is a bit higher than the minimum possible power of hit. So the initiative was not to hurt but to knock off. 
Considering everything said before, if hit into the right part effect would be knocking person off but without proper knowledge it martial arts Ron would probably just feel pain but would not get any serious injurie. Although he was knocked off his injurie would probably be concussion that would last no longer than a few minutes just enough to leave him just fine in the chambers for only Herminie and Harry to go further.
One last thing just for the Snape funs. As we know he was scratched by Fluffy at some point. He was said to “limping”, but how he should have been scratched to limp? As it turned out – not that hard. A few dip scratches that would cut bundles on his leg is enough. And as we know Fluffy is a huge three-headed dog so for him it is also not a problem to scratch Snape that hard even without struggling or repeating the movement.
Thus, we can say that he probably was not faking it, and the pain was real too. Such injuries are pretty fast to cure themselves and as we know that they are wizards his bundles were probably fine in a few days. 
These were all characters that were hurt in one or other way to gain any kind of injuries in first Harry Potter book.