Hey Bob,
Although not the best option, we had them signup with a drop down for number of children with a box to list the children's names, particularly because we have had parents signup nieces and nephews for the event that are not in F1. Then, that drop down box controls the price (1 child is $20, 2 children is $30, 3 children is $40, etc.).
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Matt Beeman
Website Project Manager, Marketing Ministries