DH and I were discussing this topic over the weekend, and we consulted the Bible, then went online to find out what other Christians were saying.
The Bible clearly states that the only way to get to heaven is by Accepting Christ as Lord and Saviour. One must understand and believe the gospel. This sounds harsh, as you are correct in that there are people who will have never even heard of the Bible or Jesus.
Acts 17:30 says "Truly, these times of ignorance God overlooked, but now commands all men everywhere to repent (31) because He has appointed a day on which He will judge the world in righteousness by the Man whom He has ordained. He has given assurance of this to all by raising Him from the dead."
I take that to mean that there was a time when God was tolerant to people's ignorance, but that since Jesus rose from the dead, the only way to heaven now is to believe and accept Jesus as Saviour.
As harsh as that sounds, I believe it to be the truth. It should motivate even more Christians to go out and minister to lost souls.
I will say that prior to my research over the weekend, I was of the mind that people ignorant to the Bible would go to heaven if they somehow acknowledged a "higher being" by looking around them at creation and nature and reconizing the majesty of it all, and that it must have been created by God, whether or not they knew that name. But having re-read some of the gospel, I know now that a person must understand and accept the gospel.
Lastly, regarding your scenario, you were saying "child" and "children". I don't know if you were referring to what happens to children when they die, but I will give you my understanding here. There is an age of accountability, which is when a child is able to understand the plan of Salvation. For some children that is very young, say 4-5 years old. For others, it is older, 8-10 years old. It depends on the child. If they have reached their personal age of accountability, and have accepted Jesus, then they will go to heaven. This concept also applies to people who have various degrees of mental retardation, or who have other physical disabilities which prevent them from understanding.
Oh, and I know not all Christians will agree with all that I have just written, and I am still learning about this topic as well, so please if anyone has more insight about this subject, I would love to hear it.