Hello fellow empty nesters! Well, full disclosure: my fledglings have returned to the nest, but their stuff really does belong to them. Since many of us are in similar situations with kids who are at home/then not/then at home again, even if it’s college, it can be confusing to make decisions about their things. Here are some questions you can ask yourself to help clarify when is it ok to donate/declutter their stuff? Personally, I would always check in with them before giving anything away, even just to get their blanket approval.

What era is the stuff from? Is it baby things, clothing, toys from when they were in elementary school? Are you *ready* to let these things go? Perhaps you would like to keep a few sentimental items. I have been taking pictures of the things that bring good memories and then letting the items go.
Is it sports equipment? Have they stopped playing that sport, or physically outgrown the equipment?
Schoolwork/Artwork – I think this depends on your own style, e.g. are you sentimental? You could try asking the kids how they feel about it as well, but my recommendation is if you are going to keep things, to narrow it down to one bin. I found this helped me make decisions about what things were truly unique/captured my kids’ personalities vs. rote schoolwork (e.g. filling in templates).
Musical instruments – Are they still playing the instrument? Will they have interest in it again in the future? Another factor is storage space since a piano clearly takes up much more space than a flute.
Memorabilia – again, this depends on both your own sentimental leanings as well as your child. If the collection consists of things that they chose to keep, then I would suggest having them cull through it.
Trophies – I was truly shocked when both of my kids independently decided not to keep their various soccer/karate/softball trophies. I thought they would want them in the future, but I guess not! If it’s important to you but not to them, you could decide to keep them, or just take a picture and let them go.
Clothing – it’s easy to process clothing that the kids have outgrown (although I have some clients who kept a few precious/strong memory pieces of baby clothing). I’m sure most of our kids change styles as they age, so would recommend that they be closely involved with anything that currently fits them.
Hobbies – do they still participate in the hobby? Will it be of interest to them in the future? My son had a plethora of the DIY kits (e.g. build your own trebuchet, pyramid, Lego sculptures, etc) that he ultimately decided not to hold on to. A discussion with them could help you make a decision.

So, if your child decides that they do want to hold on to things, it is still your decision about whether or not you want to store them long-term until they have a place of their own. My parents asked that once I got married and had my own place to come get the Barbie mansion and all the other stuff of mine in the attic. I chose to let many things go, despite the thoughts of “keeping it for my future children”. Whatever you decide, I would again encourage you to have a dialogue with your adult children so they don’t feel like their opinion about their stuff is not important.