My son has always been very interested in various things. I used to read atronomy books to him when he was 2 and 3.

After that he could read well enough to read by himself (and his attention moved to Ninjago etc.).

One thing he always liked was books from Mauri Kunnas (he did books with dogs and cats as main characters, telling about vikings, pirates, Kalevala, all the good stuff). You could check if you find something similar.

They are stories tweaked to be suitable for kids (like in Kalevala Aino didn't commit suicide but chased after Väinämöinen etc.). Little humour etc.

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And of course plain old documentaries. Kids love that stuff, or my son loves. Or if a kid can read, give them books. Proper history books, there's always some well written ones.