Jesus said, "Let the little children come to me..."
While the adults are in service children ages 6-12 will be in children's church (unless you desire them to be in the sanctuary). The goal of Jr. Church is to prepare kids to join the rest of the church in the main sanctuary as soon as they are able. To encourage this while the adults are learning in service the children are being taught a lesson from the same portion of scripture as the adults. This will allow parents and kids to discuss what they learned together.
Children should be dropped off before service starts