On my side, I think I picked the interest as my parents frequently took me to Natural Museums when I was 5 and I was super interest to dinosaurs and palentology in general at the time. We also sit together every Sat night to watch a few episodes of palentology programs (probably BBC or something else but there was many years ago). I never studied in that field but nevertheless I think that was one good trick to get kids into STEM and I'll probably do the same for mine.
What's your trick? I really believe that every kid is naturally interested in STEM but needs some guidance.
Changing the color of red cabbage juice with lemon and changing it back with backing soda. (Bonus points for the bubbles.) (Some teas also change color, but it not so dramatic.)
Magnets, lot of magnets. Make a complete analysis of every wall and object at home to see if it is magnetic, and think what is is made of. (Try also coins. Here in Argentina, some of the 10 cents coins were magnetic and other non magnetic. (Self nitpick: ferromagnetic.))
Some germination experiments. (Bonus point for spotting the difference between corn and beans.)
Watch light at night using a CD as a diffraction lattice to get rainbows. Some light have a continuous spectrum (like the old incandescent lights) and other have very peaky spectrum (like the old red/orange/yellow/green leds, or the neon lamps of different colors). (Modern lamps and white/blue leds are more complicated.)
Did you see the video of the feather and hammer in the Moon? (This in not in the DIY category, but there are a lot of things to talk about.)
For plants, I strongly believe that guidebooks like Tree Finder (https://m.barnesandnoble.com/w/tree-finder-may-theilgaard-wa...) can be a fun activity. You can turn it into a scavenger hunt or make hikes more enjoyable. There's similar books for insects and flowers as well.
For programming and tech, graphical programming languages like Scratch (https://scratch.mit.edu/) are good introductions. Oftentimes, basic math and physics concepts can be rolled in as they get older and want to create more complex programs.
Engineering has a wide variety of different kits that can be completed, but the best way is to figure out what your kid wants to build and see what you can do to make it happen.
And finally, always be on the lookout for learning opportunities. For example, my parents would let me keep the change at the grocery store if I could calculate it before the cashier returned the money.
We have science nights where kids can ask how something works and then we white board explaining how it works. Or we just pick a topic and white board it.
Lego mindstorms, check out Lego First Robotics League, if you can't find a team to join you can create your own team. They have a few options for different age groups.
Do science kits, chemistry and electricity.
Do your own experiments like rubbing a balloon then holding it by a stream of water in the sink. There are thousands of cool experiments and projects out there.
Kids are naturally interested in this stuff.
When they are a little older arduino projects are good fun for the kids and adults.
[1] Baby loves science books by Ruth Spiro [2] Books by Andrea Beaty, Ada Twist scientist etc, Grace Hopper:Queen of computer Code that I bought from Adafruit, How things work and sorry I don’t have the authors name right on hand but he has some other great books on architecture ‘built to last’ I think was one that are beautifully illustrated and fun. [3] https://www.raddishkids.com
Also, video games are really good at making them interested in numbers, calculations, etc.
Otherwise, I just take my chances when I can. When there's some interest in some random thing, I just try and run with it and encourage further scrutiny.
Everyone will show you their innate talent. Don’t be that shitty parent that has an idea of what that talent should be.
What you meant to say was, ‘everyone has a natural interest in something’, roll with that.