I started introducing the concept of “fact vs. opinion” to my almost 3YO. Probably a bit early, but she seems to be grasping it already! A fact is something that’s objectively true (I used these exact words), such as her top is blue. An opinion is what someone thinks about someone/something, and everyone can have different opinions. If her friend says “you are ugly” or “I don’t like you!”, it’s their opinion, it doesn’t make it true, and she can politely disagree. No need to be sad about it!