My kids are getting to be the age I was when I started programming.
There's also a site dedicated to HTML5 game engines, which lists popular frameworks not present on GitHub.
And, lastly, but probably the most generally useful, the Mozilla Developer Network has a considerable section devoted to games, game frameworks/engines, as well as referenced to various tools to support publishing your JS/HTML5 game as an app that can be installed/played on phones/tablets.
If I were to pick a framework off-hand, I'd probably pick Phaser.
Since the project is primarily for my kids, I wound up searching for "game creators for kids" and wound up looking at a post on Common Sense Media about game design and kids. That pointed me at Roblox, which -- honestly -- may be about the limits of their interest for now. The MMO with paid membership thing maps directly to what one of my kids has been obsessed with for some time.
Gamefroot looks potentially interesting, but Roblox claims to support Amazon devices, while Gamefroot only supports iPhones. Considering my kids have Amazon devices and not iPhones, that definitely tips things in favor of Roblox. (And Gamefroot, honestly, seems to have some load issues which would be frustrating for them.)