I wrote a bunch below, but I think most of them are probably aimed at a bit older audience, but I figured I would still post it as I really enjoy the channels and perhaps someone will like them :) (I think minute earth and Steve Mould could be suited for someone a bit younger)

• For biology I really enjoy 'Sage the Bad Naturalist'
• for engineering 'Stuff made Here'
• physics/electricity 'alpha phoenix' (I think his videos are quite technical but they are really good)
• Generally interesting/physics 'Steve Mould'
• Minute physics, Minute Earth and Minute food
• For math '3blue1brown'

https://m.youtube.com/@pbsspacetime

Great show, breaks down complex science without making it dumb, and seems to be pretty on top of the latest news.

Casual Geographic is a very funny no-nonsense animal channel. If there's a cute animal he'll remind you that it's still a wild animal that can be dangerous. If there's a dangerous animal he'll tell you how cute it is.

Not quite sure if it is suited for preteens. He talks fast and has some very creative euphemisms for killing and mating. But I'd say the humour makes up for it.

ElectroBOOM - teaches electronics and also demonstates how dangerous they can be by (in a safe-ish manner) overloading them with too much voltage or shocks himself.

The Thought Emporium - they have an overall goal of teaching a rat brain to control a robot, but make smaller videos to pay the bills like explaining the effects of radiation, looking at how long muscles and organs are "alive" after you "die", and building their own CT scanner

NileRed/Blue - heavy chemistry channel. NileRed is very structured and dry but he explores things like turning plastic into candy, NileBlue is a more candid behind the scenes look and does things like seeing how much tungstun he can strap to himself and not look like he is trying to smuggle something.

Mr Green Guy - started by being a parody NileRed, but has branched to his own thing. Mostly chemistry stuff, but has done things like seeing what would actually happen if you microwave your hand.

Explosions&Fire - another chemistry channel, Australian guy making things that boom in his shed.

AlphaPhoenix - he has a PhD in material science and builds things like a 2 million fps camera to watch a light pulse travel across his garage and a scale so sensitive it can measure a plane while it's in the air above the scale.

Micheal Reeves and William Osman - grouping these two together. Micheal makes things like a robot that removes tomatoes from his salads and a laser pointer that tracks your face to blind you. William builds things like a phone you can't drop or his own X-ray machine. Both are more comedy focused, and both are kinda not doing science/maker stuff anymore. Micheal does more streams now (dunno what the streams are like, I haven't watched one) and William has a kid and a farm now.

Stuff Made Here - He has an entire CnC shop in his basement and makes things like a basketball hoop that'll catch anything thrown near it and a .50 caliber baseball bat.

There's probably some more that I'm forgetting, I might add some more later

No specific recommendations, but make sure it's something they enjoy. Bad content will turn them off from science as a whole. If they lose interest in a creator, don't press them. Just find something else and move on.

Kurtzgesagt (In a nutshell), note, they can explore heavy topics sometimes.

The Science Asylum is a really good one for Astronomy and physics.

Some good recs here, but I haven't seen FloatHeadPhysics yet, so I'm gonna rec his stuff. Extremely good explanations of complicated physics stuff from a place of building intuition rather than throwing math at you.

i do have some for sea reptiles and dino fossils, but it seems mroe fore uni students than pre-teens.