I write kiddie stuff in French for my students and usually have it proof-read by at least 2 native speakers. Everything else, I write in my native language, English
I think that whatever language you write in, it is important to have proof-readers. I read a book off Smashwords recently where it quickly became clear that English was not her first language. There were no obvious glaring errors per se, but there were certain expressions or turns of phrase that very clearly gave it away. I look up the author's bio and sure enough, she mentions being a native Spanish speaker and living in many Spanish countries.