For real maths, 3blue1brown is my go-to (1.9M subscribers, fwiw). For "real science" with younger kids (or just non-sci/eng people), Kurzgesagt is wonderful.

For real maths, 3blue1brown is my go-to (1.9M subscribers, fwiw). For "real science" with younger kids (or just non-sci/eng people), Kurzgesagt is wonderful. And +1 for Minute Physics (previously mentioned).