My order was to pay child support for two children until they reach 18 - then if they attend college, until the age of 23 while they are in school. I have two children, the oldest chose not to attend college, the youngest did. My child support payment stayed the same for years while the oldest did not attend and the youngest did. Now I am responsible for half of the owed college tuition for the younger child. Can the past years of the over payment amount (for the older son) be applied to the currently owed tuition of the younger son?