Kiddo #1 watched me sewing, got a bit quiet and said he wished he were a girl. Why? Because girls get to do things like sew. Of course I told him some men sew, and in some cultures men knit rather than women, which cheered him up. And I promised to teach him once he was old enough to run a machine safely (I forget if I was 7, 8 or 9 when I learned? 10 with knitting though I know kids learn much younger.)
Then he asked how a sewing machine works. We found two animations online: here, and here. Timing is everything 🙂 and once it gets out of whack you have to re-time or get serviced (if you’re in Austin, I very highly recommend Maurice at City Service Sewing Machine.)
The machine I usually work on is a walking foot (though my needle moves up and down without the forward-backward motion shown in the video.)
Growing up pre-Internet, we just had a How Everything Works book, nearby library, or Dad to consult. Though most times we figured it out, animation or video (or even good diagrams!) would have been really helpful.