As mentioned before, Roblox uses Lua language which is a comparatively simpler language compared to the tradition widely used languages like Java and C++. Though obviously, it has a learning curve but there are a host of tutorials available to get one's hand dirty.
So instead of using graphical blocks to create the programs, you can let your child get the first taste of programming and incite his/her interest in a field which will be definitely useful in future.
A big advantage is using Roblox is that developing multiplayer games is muchsimpler compared to Minecraft.
While on Minecraft you have to share compiler code files to be able to run multiplayer games, with Roblox you are using the same server means that there is no need to share any file and all one has to do is to learn a few concepts specific to multiplayer gaming in addition to the other concepts of Roblox games development.
Creating a game and publishing it, then watching it being bought and receiving feedback on the same will give your child a worldview which most of us experience much later in life.
Roblox has a virtual currency called Robux which is earned when somebody buys your game and with can be bought with real world currency. This currency can be enchased for real money and can really get your kid hooked on to the field of coding.
And if you are lucky and your child a genius, you just might end up with a famous game which earns you a handsome amount helping your child finance his/her own education.
There are people on Roblox earning enough to finance their whole college degree and your child can too do some earning while learning.
Roblox comes with their own IDE where Lua is configured and your child can directly go ahead with programming. You don't need to install an IDE like NetBeans or Eclipse and then the binary required for programming like Java is required for developing Minecraft games.
Though it will definitely be useful to learn the latter but at least at the start, it is good to start with the simple tools which don't hang and are tightly build to support a particular type of development.
The team at Roblox is investing heavily in developing an ecosystem where any new developer can start quickly with their developer tools.
They have their own curriculum which children can take up to learn to code in general and specifically to get started with writing programs on Lua, the Roblox game development programming language.
I personally feel that Roblox is a great way to turn the time kids nowadays spend on gadgets into something productive.
Even if the games are not sold much, the experience of developing something and evaluating why something failed is precious to get at an early age.
Highly recommended as a starting level for any kid that might want to learn to code and is looking at the gaming industry for the same.