When people talk about nurture effects and the environment they always think of what parents say and do directly to their children, they think of violent and sexual entertainment media. It never occurs to them to think of the books children read that don't have violent or sexual content.
Some philosophers if interpreted and implemented in the wrong way could help to mold the way the child thinks in a way that that leads to a criminal or a psychopath. Some philosophers that I could easily imagine being a bad influence if the parents don't properly contextualize it are Nietzsche or Foucalt. Unlike sex or violence in movies parents generally don't worry about this, leave the books on the bookshelves, assuming that the children wouldn't be interested and that if they were it would do no harm. But the child could be interested. A particularly intelligent child or even just one with a big vocabulary may read through the books.
Growing up as a child is our most important stage of life where we learn mostly of our surrounding culture (the ways of life according to what you are told or observe). If a child learns conflicting beliefs learned from wherever in philosophy, it could affect the ethos the child grew up with or ruin his work ethics to progress in life.
However, not all the time will this be the case; depending on a variety of aspects, it is also possible that we may also benefit from philosophy such as learning a deeper meaning to life which enhances our will to strive healthily in whatever direction we choose.
So does philosophy a negative or positive thing for a child? The answer depends on the circumstances of our individual lives whether it is bad or good or the answer could be both. The real question is can you safely teach it to your child to not possibly risk his ethos? If yes, then philosophy is probably safe to teach.
It is my opnion that reading philosophy could have a negative impact on a child growing up. A child until the age of abstract reason, is very set in concrete thinking. While some children mature faster than others, there are some children that would be unable to attain the abstract qualities of thought to understand and discern higher ideas of philosophy. Children must be nutured through early stages of learning in concrete terms to allow themselves to mature into more complex ideas. Allowing children to read idealogical works that have adult themes could subject them to sexual or immoral topics that they are unprepared to handle.
To suggest that simply studying varying opinions on life, ethics, and morality can somehow taint a child is absurd. If anything, raising a child without teaching him or her that there are many different ways to look at the world, without teaching critical thinking and how to examine claims for veracity can stunt a child's intellectual growth and leads to the sort of lazy, spoon-fed, incapable student we so often see at the college level today. The majority of these students have no ability to think for themselves, to develop their own opinions, to question what they are told as "truth" in large part because they are coddled emotionally and intellectually.
It would be foolish to assume that learning philosophy would have a negative impact on anyone. Philosophy is the science of thought and it teaches people to think on their own as well as learning what the great minds of the past created. This is a foolish argument presented by someone who is not an independent thinker.
Reading something like philosophy will never leave a child with a negative impact. The child is learning and broadening their mind, if you think someone like philosophy is going to be bad for them then you might as well think that every other subject is going to leave them with negativity.
It is absurd to categorize a complex human being (no matter how young), into simply two extremely distinctive labels.
If a child is easy impressionable and had not had a diverse experience with people (of differing opinions), have a tenancy to place their opinion higher than everyone else (no matter how strong or well reason an idea is), and is highly impressionable.
Then we intuitively know that it's probably a bad idea to expose that child to works of Nieztche.