I think you are asking how children attract the circumstances of their life experience when they are too young to seemingly be in conscious control of their lives.

If that is what you are asking, then you need to bear in mind that the Law of Attraction responds to how someone is feeling, not the words they are using, though often words that are used are an indication of feeling.

So just because young children cannot articulate verbally doesn't mean they don't think and, if they think, they are receiving emotional communication from their non-physical selves regarding how their resulting vibrational output is being responded to.

If children were left to their own devices, they would naturally engage in activities that feel good to them and naturally omit those that they don't want to do. And they would naturally lead happy and harmonious lives.

What tends to happen instead is that well-meaning adults keep pointing out to their children all the pitfalls in the world around them and gradually condition the children to ignore their emotional guidance in favor of warnings about don't do this or don't do that otherwise bad things will happen. This conditioning process is what causes people to eventually disbelieve that good things come in response to good feelings and bad things come in response to bad feelings - the emotional guidance is simply discarded.

You could also be asking if children are aware of the circumstances they are being born into and, to that question, I would say yes but they are only aware in a broad sense.

It is a similar situation to deciding to go to some place for a holiday. You generally have a broad awareness of what you want to do and experience when you are there, but most people generally leave the specific details of exactly what they are going to do to the time until they actually arrive.

So why would some children be born into circumstances that seem less than ideal? The basic reason is for the experience of it. There will be something to be gained from doing so from the non-physical vantage point.

Often, you see personalities that have decided to incarnate as teachers deliberately being born into what many would regard as difficult life circumstances. This forces them, at an early age, to get clear and focused about their desires and, with that experience, they are more able to relate to others who are undergoing similar experiences. It is hard to teach that which you have not lived yourself.