It's impossible to know without watching something whether it's full of swearing or homophobic / misogynistic / transphobic hate speech.
Ads are not targeted to the actual viewer, but to some combination of regular browser user and main youtube user. this means that children will be shown ads for alcohol or gambling. (note this goes against what Youtube says here about complying with local law: https://support.google.com/adwordspolicy/answer/6012382?hl=e... Note that this is something all ad networks get wrong, and it's likely they're going to see regulation in the uk at some point if they don't fix it.)
It's hard to know before clicking a link whether it's sponsored content or not. (in the UK sponsored videos need to be clearly identifiable before the user clicks the link or clicks play. in the US sponsored content needs to be clearly identified).
If two people (eg a parent and their child) watch Youtube the recommendations fail hard. If a single person watches youtube the recommendations are pretty poor.