A good science and arts magazine for kids that age is Muse (from Cricketmedia). They have real articles, and go reasonably in depth with their subjects.
http://shop.cricketmedia.com/9-to-14-years/MUSE-Magazine-for-Kids.html
Do NOT give subscriptions to Kids Nat Geo, it's a rag fit for the trash. My 10 year old has read the real Nat Geo for a few years now. The Kids version is very sound-bitey and unprofessional - more targeted for early elementary, but I wouldn't even buy it for that age group, I would buy Ask.
Cricket Media also has literary mags for different age groups. They are an altogether stellar group.