An option you may consider, which is an effective way I have found to do the altar call is to first ask the kids who are already saved, and have accepted Jesus to be their personal Savior to raise their hands.  When the unsaved kids see how many others have accepted Jesus, they are less afraid to do it themselves.  Have them put their hands down, then ask for the kids who would now like to ask Jesus into their hearts to raise their hands and to come forward.
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