Eiswuxe, a Corona developer, posts some valuable insight here: www.eiswuxe.de/a-risky-decision/ (his blog is full of interesting posts, btw.)

Hey Philipp!

Thanks for the tip. It might be problematic especially for the Appstore as apple might reject apps due to adult ads (if the developer didn't write it in the metadata).

I've sent an email to Orly from inneractive. she is very happy to help and responds very quickly so I hope she might be able to solve this issue.

BR,
Shahar Zrihen

Small update, here are some of the relevant quotes from Eiswuxe's two blog posts on this:

"Two people complained about adult ads being displayed, which of course is totally inappropriate for apps aiming at children and so their complaint is absolutely understandable. (...)

There is however one downside to that “adult ads” story. I immediately communicated with the ad-network after users complained about the adult ads. I already ensured in the past that filters are setup so that no adult ad can slip into my apps. But somehow the filters were not configured correctly by my ad-provider. So I restricted everything that was not suitable for children by myself: ads for alcohol, tabaco, dating apps, eCommerce, business and so on. After that, my ad fillrate dropped to < 1%, and so did my ad revenue at the end of january. Seemed like nearly all ads are targeted at adults. I changed to another ad-network to see if they provide better fillrate and revenue for child-friendly apps. You will read about my experience with them in the next post!

Now one can say that two out of 2.500 users complaining is not a reason to pass $1.000 a month from ad revenue. But for me, it’s a question of principle. I would not sleep well if I knew my apps that are designed for children display inappropriate ads. Full Stop."
http://eiswuxe.de/developer-income-report-january-2012/

And in the follow-up post:

"As I told you in my last income report I have some trouble with adult-ads being displayed in my kids-apps. There does not seem to be a quick solution to this, so I decided to give paid-apps on Android a go (...) As you might understand, I don’t feel comfortable about that adult-ad stuff. "