I'm not sure of the outward context of this sentence but I assume that this is something about children's interaction with each other.
I will make the sentence more correct for you. What this sentence has is called poor word choice. While there are thousands of confusing ways to put things that are grammatically correct, not all of them are the best idea. Ill rephrase this sentence now, to the best of my ability, so that you can better understand it.
The Child's ability to discern the goal the other child is trying to accomplish, is the key element in instrumental helping.
let me know if you have any questions.