Even a short word like sin needs to be explained, or substituted with a phrase like, doing wrong. Children will respond to words or phrases which are taken from every day relationships. When the child gets over their fears they usually become very hard against the whole matter. When a group invitation is given it is too easy for children to respond, and it will often be for the wrong reason, ie. If the holy Spirit is dealing with the child they will do what is difficult, ie.
Some people give children who receive Jesus a Bible or a book.
When this is done in front of others, children may make a similar response just to get a prize for themselves. The child must be taken along with the presentation, and not rushed through the 4 steps to salvation. Keep on checking that they understand and are following. Have them restate the message in their own words. This could be staying behind, or raising their hands while all the other eyes are closed.