Including BASIC on a Commodore 64 wasn't exploitative. It was a boon, even though it burned millions of kid-hours of labor.
The reason child labor is illegal is not because we’re under the wrong assumption that work experience itself is bad for them.
Roblox is encouraging kids to develop games for a platform they make money off from. They are then paying them with in-game money to compensate them. This looks very much like a subcontractor relationship, but with payment in company store money.
They are also aware that large groups are collecting and behaving like game dev studios, and these new child developers are getting pulled in by those organizing them. There are reports that abusive behavior is occurring in these groups, but because they are not on Roblox, the company sees no problem.
You can still develop software for Roblox and never see a problem. Still, it doesn't mean that problems are non-existent.