Mommas I need help!

Okay so I have this play house from when I was a child that I’m about to start redoing to give my son for his third birthday. Originally I was going to do a dinosaur theme, buuut I started thinking about him not always being obsessed with dinosaurs and he might get tired of it so I decided to not do a specific character or animal theme. Now I need help, what sort of natural themes/decorations should I go with color wise and stuff like that?