I'm confused about what actually happened (as I think you are as well). This is most likely a CIVIL DEMAND. It has NOTHING to do with any criminal charges. You could be sued for the money... BUT the cost of them filing a lawsuit against you makes it very unlikely that they will pursue this. This is a tactic they use to get money from people who are easily frightened. If you cannot afford it, you can ignore them.
If you fear criminal charges may be brought, or if they ARE brought... call some criminal defense attorneys. I advise you and your son to not call Walmart, and not talk to anyone about this (except for a criminal defense attorney).
BEST ANSWER I got....and I hope I was HELPFUL! My answers do not establish an attorney/client relationship. Contact Steve Hamer at (214) 843-1529 for a FREE CONSULTATION.