Knowledge is useless without the emotional maturity to apply it. Ask anyone married to an alcoholic or addict!
A one-year-old may know all about how electricity works, but when the impulse strikes to stick a fork in a socket, that knowledge will mean nothing. Ask the parent of any teenage male!
Up until the age of about 6, the child simply does not have the capacity for conceptual thought. (Check out Piaget's developmental stages.) Adult knowledge is really only useful after that age.
The one effect it will have is that in the times when the child (older than 6) is calm and able to be rational, he or she will have more ability to cause havoc, because they will know how to, for example, take apart the toaster and use the heating element to make central heating for their dollhouse.
Formal reasoning "if A is dangerous, and B leads to A, then B is dangerous" doesn't develop until around puberty.
Even then, when they are capable of formal reasoning, the ability to assess risk develops much later. Brain development isn't complete until the early 20s, and until that time, people tend to take idiotic risks, especially people with a lot of testosterone in their systems. (This is why car insurance premiums are much higher when you have a driver under 25.)
The kids would behave a bit like idiot savants, or like Rain Man - having isolated pockets of extremely detailed information, but lacking the social/emotional resources to integrate that knowledge and behave like a regular adult who knows that stuff.
Depending on your definition of "knowledge", they may also behave like sociopaths, because empathy is a physically-learned skill, based on the bodily sensations that result from the action of mirror neurons.
Perhaps you are not aware, but phobias are learned physically, too. They are a physiological response to a perceived threat. The circuits that trigger phobias bypass the cerebral cortex (where thinking happens) and connect the perceptual input (sight, sound, smell, etc) directly to the amygdala (reptilian complex), which triggers the "fight or flight" response. So, "knowledge" as you define it, would not include phobias.
Emotions and proprioceptive feedback are so deeply involved in learning, making decisions, and dealing with obstacles that it is difficult to imagine how a human being could have much meaningful "knowledge" if the physical aspect of the learning process was removed. For example, children who don't crawl before they start walking have deficits in mathematical reasoning (due to poor integration of the two brain hemispheres), which can be repaired if they do a bunch of physical therapy.
As a way of resolving at least some of these dilemmas, you could consider Jean M. Auel's approach to this "inborn knowledge" in her Neanderthals in the Clan of the Cave Bear series. Children have all the knowledge of their ancestors, but it is subconscious, and they can only access it consciously once they have been reminded of it by another person. These remainders come at appropriate ages - the really dangerous knowledge is only activated after they reach adulthood and can deal with it responsibly.
