Hello Terry
Welcome new friend and thank you for coming by and posting ...
In order to answer your question, I would have to get a little controversial and delve into the beliefs of reincarnation ... which I know is a concept that many people do not accept for one reason or another ...
It is true ... when a child is born ... the child is incapable of thinking for itself ... in the conscious way we look at thinking ... so, technically you are right ... it is not responsible for it's thoughts in the physical plane ...
If, however, we look at it from a soul point of view and take reincarnation into account ... the matter changes ... It all becomes a question of Karma ...
Reincarnation believes in the principle that souls come back to the physical plane, life after life, with the sole purpose to make amends for unsolved karma from a previous life. It is, also, believed that the whole point of living in this plane is for the soul to learn something new with every lifetime it goes through, (as well as making atonements).
Furthermore ... the soul is believed to have its own knowledge which is infinite ... and coincidently, ties in with what I was saying to Nick about the conscious and the subconscious knowledge which would, also, help to explain why, every now and then, we know things that we didn't think we knew nor that we could fully explain.
Moreover, another belief is that each soul can choose where to reincarnate, the environment and the society it reincarnates into and so forth and so on.
A child dieing prematurely through disease or through other causes is all part of a learning curb for the soul in question and the souls it chooses to surround itself with. It is not a punishment for anyone nor does it punish the soul. Only the physical body suffers ... the soul continues infinately.
In life, nothing is more important than the soul because one day it will return to its Origin and Source.
Chances are that, some people would never find enlightenment if their life was easy and if the life of their loved ones was easy as well. Enlightenment is each individual's connection to whichever Divine they believe in. A child dieing is a soul trying to teach another soul something in the bigger picture.
Sorry to cut this answer short but I've just noticed it's 3.14am and I think I need to get some sleep pretty soon but this is a subject I will definately be coming back to.
Take care and have a lovely weekend
V.