Terra from Mama Says Sew guest blogs at Prudent Baby with a tutorial showing how to make a retro-inspired top for a little girl. The Peter Pan collar is all sweetness. She has a free pattern for a size 3T/4T. If you need a different size, you could probably adjust her pattern using a shirt that fits as a guide or adapt a basic bodice pattern using her pattern as a style guide. Get the tutorial.
[photo from Mama Says Sew on Prudent Baby]