My kids are only toddlers so not sure what ABC Kids was like before, but at least for the last 5 years it's been incredible. Play School, Peppa Pig, Wiggles, Daniel Tiger, Lah Lah, basically nothing but educational shows or clean entertainment (apparently vetted by educators? I can't confirm that though, just something I read somewhere).

We're pretty strict about screen-based entertainment never being wasted time and always having some practical benefit, and ABC Kids has been great.

For our YouTube stuff I simply have a youtube-dl bash script I pass a URL or playlist too and it scrapes it at highest quality MP4 then copies it to the /Kids/YouTube/ folder on the NAS, which the TV can natively play from. I'm working on a web app running local-only so we can do it from our phones too.