How are you hearing? What if I lived in a country or area of the world that outlawed Christianity and so it was scarce? I’ve been saying for years that North West NJ doesn’t have a credible Baptist Church to even learn how to desciple? So what do you do, wait till Albert Moeller to direct seminary students to the hunter lands. God has his ways and means...people don’t expressly have some preacher roll into town. Sometimes it’s reading a book, even a bible....sometimes the HS puts an idea into ones head....maybe it’s a broadcast on the radio. But my real consern still lies with people like my sister who’s brain stem was fried due to a high grade fervor or a baby who dies in infancy, or the kid in Afghan who has been isolated to the spoken Word.
First: It's spelled "Mohler," not Moeller.
Second: Have you read Romans 1?
Third: The receiving of the Word can happen in multiple ways--a preacher can preach it, someone can read a book, someone can read the Bible itself, or, perhaps, someone can see a TV program or a radio broadcast. All those would be under the umbrella of "preaching."
However, the Holy Spirit putting ideas into someone's head as you've suggested in other threads is not sufficient. In Acts, the Holy Spirit does a work in Cornelius. But, Cornelius isn't saved until after he sends for Peter and Peter preaches Christ to him. So, if the Holy Spirit does put an idea into someone's head, according to everything we see in the text of Scripture, that person will then seek out the Gospel or a preacher of the Gospel. Perhaps God will even provide a preacher (like Philip and the Ethopian Eunuch). But the idea that the Holy Sprit can save without the hearing of the Word in some fashion is simply not biblical. And, you kick against those goads at your own peril.
Fourth: As you've already been warned: Do not labor in the exceptions (such as your sister). One reason I believe that persons such as your sister are saved (even though I can't prove it in the pages of the Bible) because she could not "suppress the truth in unrighteousness" as Romans 1 says we all do. Do I think your sister and infants are given a "free pass?" No. I believe their saved by the grace of God. But their non-cognitive state (or diminished cognition, or whatever) is fundamentally different from those who have never heard. Romans 1 is exceptionally clear on this: We all suppress the truth in unrighteousness and are "without excuse."
Lastly: I would caution you on seeking to making the Bible fit, support, an soothe your own personal experience. Your experience with your sister is very heart-felt, very real, and very tragic. However, what happened to your sister does not get to rewrite the pages or theology of scripture. The "Pathos" that you feel about the situation is undoubtedly deep--and no one would fault you for that. The error comes when that Pathos leads us to say the Bible says something we want it to say rather than what it actually says. We all fight that battle. A word to the wise here, should be sufficient.
Blessings,
The Archangel