Here's how I'd do it on the cheap with a Feather Huzzah ESP8266 and no camera (which is what I have to hand):
- Set up an MQTT feed at adafruit.io (free).
- Get a feather (£19 - https://shop.pimoroni.com/products/adafruit-feather-huzzah-with-esp8266-wifi).
- Use the arduino IDE (free) to write / learn code.
- Have that code publish to the MQTT feed (free) whenever it detects a button push / body / whatever.
- Setup an IFTTT.com account (free).
- Have that subscribe to changes on your MQTT feed (free).
- Have IFTTT send notifications to your phone / email / sms / twitter, whatever (free).
All of which comes in at under £20 and proves the concept / gets you playing. Pimoroni sell a camera for your PI here: https://shop.pimoroni.com/products/raspberry-pi-camera-module-v2-1-with-mount
I don't know whether the PI works the same way as the Feather, or offers a better way of doing things. It could be that you can just send the email directly from the PI with the photo in it.
Kids are surprisingly adept at this stuff. Mine are 8 and 6, mind, but were younger when made these projects:
Presently, we're playing with a way to feed the cats from IFTTT, which means we can do it with phones, lightswitches, even the household thermostat!
All good clean fun.
(Except for the catfood)