When we are sharing Christ with children we want to communicate God's truth in love. To put it another way, they must understand what we are saying.
When a missionary travels to a far off land, he must learn the culture in order to be able to effectively communicate the Gospel message in a way that the hearer will understand. For instance, one tribe placed Judas as their hero instead of Jesus because it was their tradition to gain the acceptance and favor of an enemy and then kill them. It was impossible for the missionary to get them to see that Jesus was right and Judas was wrong. Untill... The missionary found out about an unusual custom whereas the tribe would swap a child with another tribe to insure peace. As long as they held the child of that other tribe, the other tribe would never attack for fear of their own child being killed. This child was called a "Peace child". The missionary was then able to show that God gave His Son to be our peace child, and many in the tribe received Christ as their savior.
Witnessing to children is cross cultural witnessing. There are two culture gaps that WE must overcome. If you are the typical Christian adult, you live in an educated adult culture, you have learned big words in addition to looking and behaving in an adult way. You also live in a Christian culture and use Christian terms. A child that you are witnessing to still lives in a child culture and in a non-Christian culture. They may not understand words or concepts that seem normal to you.
Example... Suppose you tell a child that God loves them, but the night before they were molested by someone that told them that they loved them. The child may then associate God with being molested and hurt. You would have to explain to the child that God's love is good and kind, and He would never do anything to hurt us, and only does what is good for us.
Example... Suppose you tell a child we are saved by faith, but they heave heard that the .... church down the road is of the ..... faith. They may associate faith with that church and come to the conclusion that only that church can save them. We need to tell them that having faith in God is to put our trust in Christ.
Example... You tell a child that he must receive Christ as their savior. What does receive mean to a child? You may have to use another word like 'take', or explain it to them. It is a good practice to use smaller words, and explain everything in a simple way.
Make it a practice to learn and understand the culture of the children that you are sharing Christ with and you will communicate much better.