While I wouldn't say I am overly sentimental, there are things I've kept from each of the kids - and things I want to keep for each of the kids. The trouble is, those things are all over the house. It's time to organize them in one place for each child -- maybe it's time for you to do the same thing.
A suitable receptacle
The first thing you need to do is identify an appropriate container for your memories, and a plain old cardboard box won't do. While you could go all out an convince your woodworking spouse to make extravagant velvet-lined carved mahogany boxes, that's not necessary, either. You need something that will protect the items inside -- and won't further damage them.
While acid-free archival quality storage boxes probably are preferred, if what you can get your hands on right now is a plastic storage bin, it'll be a start. If, after time, you realize there are items in your boxes you want to be even more careful with, you can always trade up.
Start gathering and organizing
In a 30 minutes sweep of the house and stash places, I bet you could gather most of the things you currently have and have been saving for your kids. Lay it all out next to the boxes, and organize as you place it in. If you need to, if there is a risk that someone else might look into this box and have no idea what it is, attach notes to items. I think the contents of my kids' boxes is pretty obvious, but I am adding notes anyway, just to be sure.
If during this process there is something that you think might not be worth saving after all, now is the time to throw it away or recycle. You can end up doing some excellent cleanout during this process.
Once you've got everything together, put the boxes in a convenient place. You want to be able to get to them and add to them easily. No more stashes of stuff all around the house! When things present themselves that you think you want to save, put them right into the boxes. (However, this might also necessitate a yearly review and cleaning out of the boxes.) One thing I plan to do going forward is add photo albums to each box. With electronically created albums and online services, I wait until there's a good coupon code, then order copies of vacation and holiday albums for each child.
When I look at what I've gathered for each of my kids, I'm filled with nostalgia -- but I also know these kids are going to appreciate what I have saved. Key elements of their childhood and our family life, conveniently organized. Someday, of course, I'll hand over each of their boxes. Until then, this is just as much for me as it is for them.
For more tips on preserving memories: