Selling an Alienware 5600X (6 cores/12 threads) computer with an older GTX 970 w/4 GB. (3.5Gb actually usable.) This would be a fine machine for a youngster. The 970 is still a reasonable 1080p card, and will run games like Minecraft very well. I think Roblox would be good, too, although I haven't tried it.
The system has 32G of RAM and a 2TB Adata-brand SSD. I can replace the Adata with a brand-new Samsung 990 Evo 2TB for an extra $50 if you want it.
It works perfectly, runs quietly, and comes with Windows 11 Pro installed, activated, and with all the drivers current. I can install something else if you'd prefer.