We have under bed storage bins from ikea that their keepsakes are kept in, and a gallery wall in our main hallway where I frame some of their big art projects. Anything in between gets some time on the fridge and then is buried in the trash so they don't accidentally find it.
Something that really helped when they were little and churning out coloring stuff was hanging their art facing out to the street on our enclosed porch. I usually did seasonal or holiday stuff and didn't feel bad about tossing it all a few weeks later, they loved that everyone walking by could see their masterpieces.
We went through the big folder that came home from school together, kept a few favorites, and toss the rest in the recycling bin. It’s just too much and it’s a good life lesson to learn how to thin out treasures and to toss stuff. As a mom, I do the hard de-cluttering for the whole family but I leaned into teaching it a bit, too.
“We care about people, not stuff” was a good saying. It also made keeping things easier to cherish and easier to find.
But for the sculptures or physical things, we have one shelf on our bookcase that she can style as she'd like, but as she runs out of room, she has to remove items that aren't as important to her anymore. That puts the decision on her which helps. That being said, I do keep the really cute/impressive pieces 3D items. Like she sewed a stuffed animal of our dog in a class this past year and I love it, so once that is removed from the shelf, I'll hold onto it. I have a small box (like banker sized) for things like this.
I only have one kid, but I put some of my favorite paper (flat) art on the inside of our kitchen cabinets. The kid is 17 now, but I still love seeing drawings from grade school when I open the cabinet.
I hang my favorites in our ridiculously giant master closet. The closet can fit our DS' twin bed without all of our the clothes and stuff. When we toured our house in the home buying process H and I literally said that to each other.
The stairs leading to our finished basement has a sort of ledge, where we’ve put some 3D art stuff. The walls in that stairwell are also where some of the flat art projects hang. It’s mostly been enough area to keep things, although there are a few framed art pieces/canvases in my office and a few 3D pieces on the TV stand.
for 2D items (lol) I frame a few a year that we hang in the hallway, though we are only done with grade 2 and getting close to capacity lol. Small hallway. A few others throughout the year I keep in his "memento box" and the rest gets trashed.
Any 3D items (sculpture things) that are good get displayed either in his bedroom or at on our end tables, etc. So far, very minimal, he is not super crafty.