In YouTube, there's a notification or warning if a video is not suitable for young people like below the legal age. I think it's the parent's responsibility to always watch their children's activities online.
I also do remember LL Stylish promoting Stake on his twitch while playing league of legends. I'm not against it but he should've considered his audience which is under 18 mostly and he had over 10,000 Viewers at the moment that advert went online, Not counting his Youtube video containing the same Ad had over 200,000 Views, Casinos can't be blamed for it if the will power of people running streams isn't strong and they're easy to give in to these temptations.