As children often do, Paddy tends to gloss over some things the adult reader can see are serious. But he also exaggerates other things.
When Paddy is injured by debris left by builders, his understated way of telling us the facts conveys a graphic intensity, "My foot was wet. My shoe was full of blood."
The short matter-of-fact style in which he speaks seems to understate what sounds like a terrible injury. This shows that Paddy is used to experiencing and seeing injuries and wounds during the often dangerous play with his gang.
It may also portray how children very often don’t realise how serious injuries are, which leads to adult panic when they are discovered.
Conversely, we see that Paddy exaggerates at times too. When he gets into trouble with his parents and they discipline him, he often describes their reaction using hyperbolic idiom – for example, “I got killed”.
Obviously, this is not literal. It is an idiom used by many people to emphasise the harshness of a punishment.