Child rearing is not straightforward.The question of whether parental neglect causes behavior problems presupposes we have a very clear understanding of (a) what children need to thrive and (b) can accurately determine cause-and-effect when their needs are not being met. Unfortunately, we do not have such a clear understanding of human behavior, certainly not with children!
Firstly, there are many, many, many different ideas about what children need. Different eras have had different ideas . We are all too familiar with the changing opinions of child health. Many parents have seen ideas change in their lifetime: from how to discipline, to what is a good diet; from whether to breast-feed, to how to toilet train. No doubt in the future we will consider many elements of today's best-practice as totally appalling!
Secondly, we also see differences across cultural, social, political and religious dimensions. We simply differ in how we think we should care for children. The post-modern world abhors "absolutes" - things that are true for everyone, universally across all time and places; and it abhors "absolutes" when it comes to raising children. We can be sure that somewhere in the world there will be someone who disagrees with our ideas! We even differ in what we consider to be a child, for different purposes, in different countries - when a child can marry and so on!
These different opinions in child-rearing and lack of universal norm creates great problems for conceptions of "neglect". For example, in one country a child must start school (or homeschooling) at 4 years of age; and in another 7 is the legal age. Parent's of a 6 year old child, unschooled, would in the first country be guilty of "educational neglect" (and probably the child could be removed from the family);while in the other country they would receive all the blessings of the state.
Of course there are some international "similarities" in ideas about child-rearing.The 1989 United Nations Convention on the Rights of a Child is one legally binding international document signed by hundreds of nations that does capture international agreement. However the agreements are high-level and general, implemented different ways in different countries , and still cause formal notions of "neglect" to vary widely.
With "neglect" such an ill-defined, variable concept we are on shaky ground to start making conclusions about cause-and-effect between some area of behavior and "neglect". Even with legal definitions of neglect, we would be hard pressed to prove causal relationships. In fact to jump to conclusions is not only wrong, but potentially dangerous for the child because we run the risk of TOTALLY missing what it is the child really needs.
To understand children's behavior we need a far, far broader perspective. Focusing on our own narrow ideas about what children need; and even legal defintions of "neglect" will not help us solve the behavioral, social and personal problems that plague children across the world. Indeed it is often children of the Western world - children who are legally not neglected at least by OUR standards - who are most severely affected by "behavioral" issues.