Kids are packrats, generally. They hate change. My mom is not a packrat, and painfully to me at the time, decluttered tons of stuff I wanted to keep. Now I am grateful. Not only do I not have the burden of all this sentimental stuff (take a photo as Erin suggests), but unlike so many of my friends, I will not have a seriously cluttered house to deal with when she dies.
I do not have my own wedding dress--which was blue velvet and street length--I might theoretically have worn it again, but didn't, so it went.I am still married to my first husband after 20 years. We are still struggling with different levels of, uh, archivism. Nonetheless, I have learned a lot about keeping only the things you really use around you and saving space for future good things to come my way.
If you keep, say, a wedding dress, which is bulky and tricky to really keep usable, you are setting up an expectation, perhaps, that it will be worn, and that the person who would be wearing it will fit into it. I say let it all go. Take a photo.