Yup! we can not control the content creators forte that they want to show on their channel, that is why as a parent I think we should be the ones that are guiding the little ones in what they are watching.
^ I definitely agree with you, we can not blame social media like Youtube because that is a part of their marketing strategy, so the best part here is the parent should always watching parental guidance for their children and avoid possible involvement in gambling. There is nothing wrong if they are aware of gambling as long as they will not be under influence of it and start to gamble on their own. I don't know how youtube filters their video, but I think it is good for them if they will not allow to 18 years old below to see a gambling video.
Social media shouldn't be the one to blame there will always be content that is not really suitable for children, and social media platforms can not control all content that has gambling, explicit content, and NSFW, so I think the parents' cooperation is surely be needed.