This is so subjective. Do you want a calm sage green? A bright green? An evergreen? A blue green? What is the vibe here? Do you have any bedding picked out yet? Sometimes easiest to get bedding and match the paint to it. My friend paints her kids' rooms with Ecos lullaby paint because it is non-toxic. They have a limited color selection which really helps narrow down the choices.

Find the bedding first. You might go off on a different color entirety.