Oftentimes this is the case these days. The kids are now grown and have gone off to university, moved to their first apartment, or have even married, but much of their personal “stuff” is left behind.
In some cases the intention is that a lot of their valued personal items will eventually be moved to their new location, but can’t be relocated immediately. On the other hand, if your children’s belongings have been stored in your home for years, it’s likely they haven’t given these items much thought and aren’t all that sentimental about them after all.