[ObsoleteNerd]

youtube-dl is your friend. Build a local folder of shows you approve of and let them access that.

The Internet is an incredible tool for parents, with endless educational and legitimately beneficial videos, but there's so much noise (and malicious intent) to filter through that it's absolutely never worth trying to blacklist stuff, just block the Internet entirely and locally cache anything relevant until they're old enough to understand things better.

We have an RPi plugged into the TV with a folder on a USB stick, shared on our LAN, where I can use youtube-dl (command line or the GUI) from any computer to scrape videos we've found for the kids. They go straight to the shared folder, and she can access them on the TV or our phones via VLC. I then keep a couple dozen specific favourite videos on my phone's SD card for "emergencies" (road trips etc).

She gets to watch shows without us worrying, and doesn't feel like she's missing out when friends talk about YouTube, but we don't ever have to worry about what she's watching.