Organization
It is an art and a skill to be organized. Some are great at organizing their space while others are better at organizing non-tangibles. I am pretty well versed in both but have learned over the years that having less requires less organization which leads to more free space and time. It can be hard to let go of those things you think you will need later or the memorabilia you have collected over years. I personally struggle to let go of my kids artwork, their keepsakes and photographs.
I like the idea of them having a chance to decide for themselves what has meaning once their adults. Also it allows me to recall those special moments and memories from their childhood. When was the last time you explored your closets or garage and discovered some remanence of the past long forgotten? If not, maybe you will be able to let go of the clutter that has collected over the years. Either way letting go and taking the time to sift through all that stuff requires organization.