Garwoofoo
I think every parent knows that YouTube is an absolute minefield when it comes to kids' viewing.
Luckily my boy is pretty restrained in his tastes (so far) and hasn't gone off piste in terms of viewing (that I am aware of). His viewing diet has consisted mostly of Super Smash Bros videos over the last few months, which occasionally get a bit excitable but not in any way unsuitable for him.
Recently he's been branching out and we've found a couple of entertaining channels:
Joseph's Machines
https://www.youtube.com/channel/UCbNvfx3rYYxEopnRGxfu53Q
Joseph creates elaborate, entertaining Heath Robinson-type machines out of household instruments that usually involve him accidentally destroying his room or narrowly avoiding serious injury. His automatic hair-cutting machine (key feature: steak knife attached to high-speed fan) makes my eyes water. But I particularly enjoyed his cake server:
Backyard Scientist
https://www.youtube.com/channel/UC06E4Y_-ybJgBUMtXx8uNNw
On a similar note, but more destructive and definitely more insane, is this lunatic who builds things in his back garden, usually involving high-velocity projectiles and/or things on fire. He is definitely going to kill himself one day. But there's some real science going on underneath all the chaos. Enjoy some real-life Mario fireballs:
Anybody got any other suggestions for channels that are both fun and educational?