For children in the developed world their Roblox earnings are likely non-essential. If they don't want to work on Roblox mods, or whatever they do, then they just won't. Forcing your child to work on Roblox would be straightforward abuse same as any other kind of abuse.
For children in the developing world - perhaps there are some for whom Roblox development is mandatory. But, would that child be better off if we deprived them of Roblox? Wouldn't they just work somewhere else in worse conditions in a career with less of a future?
I don't see why kids earning money from Roblox is bad. The efforts to criticize it strike me as pattern matching. Child labor = children working in coal mines or as chimney sweeps = bad. Kids making Roblox games for fun is child labor therefore kids making Roblox games is bad. Doesn't strike me as a compelling argument.