These girls' hairstyles were mostly done at Disney resort salons (Bibbidy Bobbidy Boutique; Disney Studio 365 etc), also called Princess Makeovers, but would work well to be redone for fairy and princess costumes, respectively. Some clearly have hair extensions added, which can be purchased fairly inexpensively at Target, Claires, etc.
This cute girl got a full 'Princess Makeover' (Tiana-inspired), including face paint, which her mom posted on disboards.com (follow link to see more).