It's not about keeping children out.
It's about making a non-child-safe-place child-safe by additional means, so parents can let their children interact with it, with minimal supervision. It's the modern version of parking your children in front of a tv that only has a few channels tuned.
That those additional means can be circumvented, is another story. Letting 8 year old children interact with media at all is also another discussion.
If you want to give children access to media that is rated for children, that can be done on some platforms. Like Steam. Steam is a closed platform. Everything there is curated and evaluated. Even if it does not have an official rating. And you can have a parental controlled account, where you can approve addition play time, purchase of things, and all sorts of configuration.
But doing so on Itch is just not doable with a reasonable effort, and the wallet idea acutally makes it impossible. Sure, if you put unreasonable amounts of effort into it, one could cobble up something to only show curated web games. But imho it would be easier to just create a new portal entirely. Or use the existing portals that aim to be child appropriate.