I'm in the same boat as you on not knowing much about child labour.
That being said, if a child is doing labour for a company (in this case Roblox, but the same could be said for Instagram, Tiktok, etc.), why is it considered more ethical to NOT pay that child for their work?
I know an argument could be made that adding financial incentives encourage more kids to participate in said child labour, but NOT paying them doesn't dissuade them from doing so.
And how is Roblox's practice different from the creator funds of social media sites that rely on user-generated content to justify their existence? It's all very murky to me.
I think my problem with this model is Roblox taking such a large cut from their workforce, not that they pay them at all.