We've lived in our current house for 3 1/2 years. We are painting the last child's room right now. And that should be good for....the next 20 years, LOL.
DD, age 22 months, had her room painted before she was born. It's a neutral color so we can accessorize with colors she likes for bedding/curtains. I have 3 quilts made by my grandma (her namesake, Sara) and hope she wants to use them. All 3 have different shades of pink.
Oldest son, age 7, had his room painted last year. A darker blue/gray that should age well. He has a Star Wars theme and just got a new comforter for Christmas. DH had old framed Star Wars posters from his childhood so he gave those to DS.
Middle son, age 5, just had his room painted...last week, LOL. We've been working on it for almost a month. It's a brighter blue, more of a royal blue, which should also last for many years. He also got a new Star Wars comforter for Christmas but has 2 framed superhero posters (found at a garage sale for 50 cents each!!!). So he has Spiderman, Batman and StarWars all in his room.
As the kids age out of "themes" I can easily replace with plain bedding and put other pictures or posters on the walls. I have the frames and posters are cheap so an easy update. Painting is pretty inexpensive but time-consuming so I hope we are set for many years. I have nice wooden blinds so no other window treatments which keeps things simple.