Is the game Garry's Mod appropriate for children?

It is a bit more violent than minecraft. I would suggest being 12+ to play it

It's not like Minecraft. It's more of a sandbox game rather than a survival game. You can build complex machines and things like that. I think a kid would have fun with it

Yes its fine for kids, however online experiences can wildly differ, but the offline game itself is perfectly fine for anyone of any age.