Winter would probably make her younger self hot chocolate and be like,
"It's going to feel like everyone is going to hate you, even your sisters, and you're going to hate Uncle Winter for awhile, but its not your fault and you have your place like everyone else. Also this thing called Christmas and snow days are going to really pop off someday and people will start liking you and it'll make Spring super jealous."
Tiny Winter would probably feel pretty confused and worried but will nod her head and ask to go sledding with her older self.
Mago would probably tell her younger self that she's going to stop being a scaredy cat and even love scary things. And that she should embrace her powers and never feel bad about using them. And that she's going to meet people with powers like her.
Little Mago probably won't believe she'll ever like scary things, and maybe not even believe she's talking to her older self, but will be intrigued about meeting people like her. Then both will probably make illusions of butterflies for fun.
Felix would just cry. His younger self would probably then give him a bowl of milk to make him feel better