Minecraft. My kids, a bit younger than 7, are ridiculously creative with it. They’re always making redstone music machines and piston machines.
The best thing about Minecraft is that it naturally scales to their skill. They began just learning the controls and exploring. Then made simple houses. Etc…
The older one is so hooked he builds his own mechanical pressure plates and pistons with Lego.
Do try to use Java Minecraft if you can, because modded technical Minecraft will last forever. Once you’ve “beat” the base game move on to things like GregTech and it’ll never end.
There are two versions of Minecraft. Java version is the original Minecraft, but Microsoft rewrote it and called it "Bedrock" for Xbox; this version is ported to a number of platforms including the PC. It supports "data packs" which can change the game but not as extensively as "mods" for Java Minecraft.
"Technical Minecraft" involves building various machines in Minecraft; either in vanilla (unmodded) using red stone, water, and other properties of the game itself to do things - some are quite complex, but they can include things like intelligent mine cart routing, strip mining, and resource sorting.
"Technical modded Minecraft" involves one or more of the "tech mods" which MASSIVELY increase the complexity; one of the most famous is GregTech, which adds machines and electricity to power them.
Arguably the most complicated tech modpack is Gregtech: New Horizons which has you start out digging dirt with a stick and ends up with you on various planets searching for materials. It approaches and scratches the same itch as Factorio or modded Factorio (and arguably is somewhat like Satisfactory). End-game often involves optimizing the setup to reduce load on the host computer itself.
There are also modpacks with similar depth focused on magic; but the two become mixed.
The cheaper bundle includes both versions, which is nice. You need one per simultaneous player (so if you have two PCs and want to play with your kid you'll need two copies).
You can make the Java client "host a server" (open to network) which is fine for basic play and starting out multiplayer; but you can play single player with no server at all.
The server is nice (and free for Java if you have a machine to spare or even some CPU) because you can make a "persistent world" that's always there whenever someone logs in. But that can all wait for later.
It's possible to play local multiplayer without a server. One player can host the game and "open to lan." You will each need your own Minecraft license.
The best thing about Minecraft is that it naturally scales to their skill. They began just learning the controls and exploring. Then made simple houses. Etc…
The older one is so hooked he builds his own mechanical pressure plates and pistons with Lego.