"The man reads to the boy."
Translation:Mannen läser för pojken.
I know I'm super late to this but I think I read one of the community contributors' comments on a similar question and they said that "at" is like "im doing this for you because you can't" or in this context it'd be more because you don't want to. I'm still trying to figure out everything, these mods and community contributors keep adding in things in random places so I keep checking each one of these forums for explanations.
There are generally translations between pairs of prepositions that are the most common. For instance, "on" tends to be "on" in most languages - but then again, sometimes it's "in" in another language, and although there must have been some logic to it at some point in time, that logic is often seemingly completely aribtrary nowadays.