It is legit and an excellent route into developing games.
Yeah.. it’s not quite that though. It’s an online gaming platform, where you CAN make your own games and publish them, but chances are your kids will just want to play the millions already there.
There are lots of grownups on there and you do need to be careful, but they make it easy to do. Keep track of their their friends list and make sure you know who they all are. They do get random friends requests from strangers. I think you can disable chat – there are lots of safety controls on there.
In terms of developing games – it’s not particularly kid-friendly. It’s similar to doing Javascript in a web browser. And don’t link anything to a credit card FFS, that’s just asking for trouble. Give your kids their own Google accounts and their own accounts on the computer you’re using.