Fantasy kids books, e:g Tolkien, CS Lewis (Narnia), Joan Aiken, Edith Nesbit are timeless though right? Then there are books set in a different time, that kids still enjoy e:g Just William series 1920-60 (which contains some stereotypes about race or gender roles which can actually lead to a healthy discussion about to what extent we've moved on and "don't say those sorts of things" nowadays) . So, books set in the current decade are great but kids can have a lot of fun reading older stuff if that isn't available. Ours read quite a mix of old and new.