Ok so having NEVER heard of this I did some research and it seems it could come from problems with potty training. Actually glad this came up and I'm going to remember this when it becomes time to train my grandson. I hope you can learn to accept this, but sorry, I think I might seek mental health treatment for him. Just my opinion, don't mean to offend anyone.

I understand how conflicted you must feel and can see how the other thread doesn't help you from a parents perspective. I wanted you to read it, so you could understand the fetish more. I think it might be helpful to handle this from the view - this is a private fetish he should use discretion with. Most people don't share this fetish with loved ones unless its a partner who accepts it. Your son needs to accept this is you /your wifes house and you don't appreciate baby furniture being set up and you also don't want him to do this around the family. How on earth is he going to sit n a highchair?

For example if your son likes snakes or guns but another family member isn't comfortable ...then he shouldn't buy guns/snakes. If you and your wife are into being swinging - you're not about to bring the couples into your house. If he wants to wear diapers in private, then fine but he needs to do it in private minus the furniture. No I don't think you're old fashioned - this doesn't fall under that category lol.