Breadboards[1] with breakout boards[2] (the Pi Pico in particular is incredible, having an unusually detailed and correct datasheet). MicroPython is probably a great way for gets to get started on the compute side of things. Once you have something working on a breadboard then you can "graduate" to PCB design (and there's nothing wrong with designing the PCB to take a breakout daughterboard) - possibly perfboard as an intermediate step. Use KiCAD - it's Blender-tier open source software. A high quality breadboard and wires are very important - I guess diagnosing a loose connection is a learning experience, but it would be an overall hindrance to learning if encountered frequently.

Have many spares of all components (including breakout boards) handy - they will probably summon the magic smoke a few times.

They will likely quickly need to learn how to read data sheets. You can often get away with copying the "typical application" and avoiding the real technical stuff.

Friendly reminder: those brains are still developing. Adequate exhaust is extremely important (even if you are using solder-free, flux fumes are varying levels of toxic). You want those fumes going out of the window, not via a filter into the same room. Any complaints about headaches are serious: you aren't extracting the fumes correctly. There are a few important things to know about soldering: "there is no such thing as too much flux," "solder likes to flow towards heat," and "heat the thing and apply the solder to the thing (not to the iron)" (to keep the technique at its most basic).

The often recommended Hakko FX-888D is just plain awful. The Pinecil is way better (yes, even though its a fraction of the price) or the TS100/TS101.

[1]: https://en.wikipedia.org/wiki/Breadboard [2]: https://www.raspberrypi.com/products/raspberry-pi-pico/