The filing of criminal charges is a decision made by the district attorney or city attorney, not walmart. I have never heard of a case where walmart filed a civil lawsuit over non payment of the demand. You are under no obligation to pay the demand and it is not money owed. If the merchandise was recovered without and damage to it, then they have suffered no damages so would be difficult to obtain judgement of any value...especially from a young person as they normally do not have a lot of assets.
Answers to AVVO questions are for general purposes only and do not establish an attorney-client relationship. This answer is not a substitute for legal advice and should not be relied upon without a full consultation with an attorney that can fully look at issues involved.