"The laws have obviously not prevented children from working in the entertainment and fashion industries"
They were never meant to. What's the point in even saying that? Child labor laws still affect how long children can work, when they can work, what kinds of things they are allowed to do. And its compulsory for children to still get an education even when they have a job.
"Thus, child labor laws have played a large part in so many child stars becoming ruined, impoverished adults."
The solution to which is not getting rid of all child labor laws. The existence of exploitation means the laws need to be improved not repealed. Also, just because children are exploited in one industry does not mean child labor laws as a whole are flawed.