In the books, Harry consistently takes seemingly Muggle routes to Platform 9 3/4, to Hogwarts by train (which has been boarded before), or at his place on Privet Drive, (just to name a few of the times) as it seems that he was (nearly) unprotected (magically) most of the time.
Why don't the DE just Apparate in and kidnap him while he's at his most vulnerable?
Edit for clarity: Per the comments and answers, Voldemort was highly against any of the Death Eaters killing Harry, but why not kidnap him directly, rather than put his name in the Triwizard cup? For instance, why not on the train to Hogwarts among other such places? I have reworded the question to lose the specifics (as they seem to get my questions in trouble) and make it more general. I hope this clears up some of the confusion, but if anyone has any edits to make this question more legible, I'd be more than happy to see them.
Also to note, there is protection against Harry dying at Privet Drive, but kidnapping is not listed as something that can't be done from what I can deduce. There may be evidence to the contrary, but I am unable to find it.