Your son might not have an entrepreneurial desire but you probably know some young person in your orbit who would be interested in the experience. If you offer them the opportunity to run the store (selling through the remaining stock) maybe you’ll spark something that’ll turn into something great. Maybe there’s a youth club or student organisation that might be interested?
Giving away the stock / selling it on Amazon FBA / wholesaling it is a good way to get rid of the stock but it doesn’t take advantage of something rare you have: an online store with a product people actually want. The money side is a wash — the product is a niche gimmick — but it doesn’t need to be a financial success to provide value to some other kids.
(Plus, if you do bring some other young entrepreneurial spirit into the project, you’ve got an option on their future success: if you become the spark that turns them into a great success in future, the returns will be huge! The next jeffy bezos could owe you a lifetime debt of gratitude.)