Having lived among and served refugees for many years, while living near a large refugee camp in Austria, I have a heart for any tale that helps others understand the difficulties of adapting to a new culture and land. I look with sympathetic eye towards differences in cultural practices. However, the protagonist, Onion John, holds many quaint folkloric beliefs that, as a Christian, I certainly disagree with . They are not simply a culturally different way of doing things, they are untrue. Onion John portrays superstitions and even mild occultic activity as simply outdated but otherwise neutral. Andy's parents have no objections to Onion John's beliefs and practices per se; they simply object on the grounds that they are not "scientific" - a point of view I would disagree with as much as Onion John's. I would want to compare folklore, superstition, occultism and rationalism with Christianity as my child read this book or, preferably, as I read it to her.
Closer to home for most readers, is the book's focus : you don't have to be like everybody else. As parents, we all want our children to be strong enough to resist negative peer pressure and Onion John provides some great fodder for discussion of times when it is best to march to the beat of a different drummer.
As the story unfolds, Andy grows up and faces choices about his future. Revolving around these changes is a lovely secondary theme related to Andy's relationship with his Dad. Andy clearly cares loves his parents and cares very much what his father thinks about his friendship with Onion John. As one Mom who uses BookAngles commented, "What kid hasn't gone through a time when his/her parents disapproved of his/her friends? I think every kid can relate to that." This is resolved in the book in a way that strengthens family relationships rather than damaging them. In a touching moment near the conclusion, Andy tells his Dad that he wants to be just like him. What parent wouldn't treasure such praise?
While it contains some definite "parental interaction needed" elements, Onion John is well written and thought provoking. There is excellent fuel for discussion about the worldview of both Onion John and the Rusch parents. Should parents wish their children to read Onion John, I'd certainly recommend parental involvement.