At the fall Raspberry Pi Workshop, I mentioned a weather station kit for the Raspberry Pi. The kit that I had in mind was developed by the Raspberry Pi Foundation under a grant from Oracle Corporation and sadly, is no longer available.
If all you want, or if you want to start with, temperature, pressure, and humidity, the Sense HAT will do that. I did a little poking around, and found a complete weather station kit here: https://shop.switchdoc.com/collections/raspberry-pi/products/ourweather-complete-weather-kit I haven’t tried this one myself. I did read pretty extensively about it. The kit does not include weatherproof enclosures, although there’s a parts list and instructions for making the outdoor components weatherproof. I also found a comment that the rain gauge must be mounted absolutely level to work reliably, which argues against pole-mounting it.
The outdoor instruments are available separately from a variety of sources, including Amazon: https://www.amazon.com/WeatherRack-Anemometer-SwitchDoc-WeatherPiArduino-Raspberry/dp/B00QURVHN6/ Sparkfun has the same kit, but it’s out of stock. The wind vane is essentially a resistor network, and I’d think that an A to D converter IC would be the right way to tackle that one. I haven’t tried it, but this one looks promising: https://www.adafruit.com/product/935
The instrument set doesn’t include temperature or humidity sensors, but they’re inexpensive: https://www.amazon.com/gp/product/B0795F19W6/ Sensors that include barometric pressure are available: https://www.adafruit.com/product/3660
So, if your kids are pretty motivated, you might get them a box of parts and see how they do, perhaps interfacing one sensor at a time so there are successes along the way. If they’re more interested in the final result than the process, or if the goal is to study earth sciences, then the SwitchDoc kit might be the right tool for the job.