After watching my kids (2 and 4 years old), I can tell you that there is nothing more upsetting than:
- Not being able to do what you set out to do (open a package, connect a Lego, etc.)
- Being told the world will be one way and then finding out that it’s not
- Not getting enough sleep
- Being hungry
- Someone else taking something that’s yours
- Not being treated equally (with your sibling)
- Losing at Uno (ever)