Today is a real nail biter of a topic. My 4 year old son is very impressionable and enjoys reinacting stories he hears. Needless to say, we glossed over the whole "Abraham is going up the hill to sacrifice Isaac" thing and instead focused on Isaac's obedience to his father, and Abraham's obedience to God the Father, and how these things are one and the same in God's eyes. We compared it to Jesus obeying God the Father and carrying His cross. Obedience rooted in love is so, so pleasing to Our Lord!
The faith and obedience of Abraham is proved in his readiness to sacrifice his son Isaac. He is stayed from the act by an angel. Former promises are renewed to him.
 After these things, God tempted Abraham, and said to him: Abraham, Abraham. And he answered: Here I am.  He said to him: Take thy only begotten son Isaac, whom thou lovest, and go into the land of vision: and there thou shalt offer him for an holocaust upon one of the mountains which I will shew thee.  So Abraham rising up in the night, saddled his ass: and took with him two young men, and Isaac his son: and when he had cut wood for the holocaust he went his way to the place which God had commanded him.  And on the third day, lifting up his eyes, he saw the place afar off.  And he said to his young men: Stay you here with the ass: I and the boy will go with speed as far as yonder, and after we have worshipped, will return to you.
 God tempted: God tempteth no man to evil, James 1. 13; but by trial and experiment maketh known to the world, and to ourselves, what we are, as here by this trial the singular faith and obedience of Abraham was made manifest.  And he took the wood for the holocaust, and laid it upon Isaac his son: and he himself carried in his hands fire and a sword. And as they two went on together,  Isaac said to his father: My father. And he answered: What wilt thou, son? Behold, saith he, fire and wood: where is the victim for the holocaust?  And Abraham said: God will provide himself a victim for an holocaust, my son. So they went on together.  And they came to the place which God had shewn him, where he built an altar, and laid the wood in order upon it: and when he had bound Isaac his son, he laid him on the altar upon the pile of wood.  And he put forth his hand and took the sword, to sacrifice his son.  And behold an angel of the Lord from heaven called to him, saying: Abraham, Abraham. And he answered: Here I am.  And he said to him: Lay not thy hand upon the boy, neither do thou any thing to him: now I know that thou fearest God, and hast not spared thy only begotten son for my sake.  Abraham lifted up his eyes, and saw behind his back a ram amongst the briers sticking fast by the horns, which he took and offered for a holocaust instead of his son.  And he called the name of that place, The Lord seeth. Whereupon even to this day it is said: In the mountain the Lord will see.