You can choose a color, draw, and erase the whole canvas. That's all. Tested by my 2 year old and 4 year old. My 9 month old thought the screen was delicious. I tried to find a drawing app simple enough for young kids to use without supervision, and everything had way too many features, or ads, or cost money. So this is my solution.
Choose a color by tapping the color palette; the border color will change if you drag your finger on it to show what color will be selected. The app is fullscreen, so you have to swipe up or down from the bezel, but I've also added black bars at the top and bottom so kids are less likely to accidentally bring up the system controls. Tap the recycle icon three times to clear the screen. And you can use the Android built-in screenshots (power + volume down on most devices) to save a picture.
Please give me feedback, especially if you hit crashes or glitches. I purposefully didn't include crash libraries so the app size is really small and doesn't need internet access. And let me know if you have suggestions for usability for young kids. But bear in mind that additional features means adding gestures or icons that could over-complicate things for the average toddler. Thanks!