The Lola Lago detective series is good--
https://www.eurobooks.co.uk/language.../m4/c21/6/LLDE
So is the Manolito Gafotas series--I heard it called the "Wimpy Kid" series of Spain although it is not fair to compare it exactly since it is unique. But it does have that age appeal and fun to it--
http://www.clubmanolitogafotas.com/
Both series are written in Spanish, not translated.