Hopefully Wal-Mart will make new glasses for the boy free. I would speak to a manager about the situation and see if they are willing to do that. I assume the boy sustained no injury by wearing the wrong glasses, in which case you might pursue an injury claim.
I am not sure there's anything actionable here. Unless you can show damage to his eyes which is not correctable, it does not appear to me that this is case worth pursuing. Perhaps Walmart will consider helping you with the expense of the new parable glasses.
DISCLAIMER: This does not constitute legal advice. By providing the requested information you are not entering into an attorney-client relationship with this law firm. Only a written retainer agreement between you and our law firm can create such a relationship. We are only licensed to practice in NH and Massachusetts.
Walmart should replace the lenses with the correct prescription at no charge. Speak to the manager. If he has suffered any long term damages to his eyes then speak to a local personal injury attorney.
A roundup of the best tips and legal advice.