Why do I have to pay arrears for a kid that was adopted and another one that is deceased?

Because the court ordered you to pay a specific amount periodically until either the child reached a specified age or was no longer eligible for support. If you fell behind prior to that time, then you have to continue to pay the arrears.

Both children are, or were, your children, adopted or not. Therefore the child support was due and payable for the time for which it was owed. The fact that one of the children died after the fact does not change the fact that he or she needed support during the period in which you should have paid.

The arrears on the child who has died will be owed, it was due during his life. All current support stopped at this death.

On the adoption, if the arrears were dismissed, it would be stated so in the adoption paper work, review your copies.