Of course, when it comes to choosing colors for a kid's room, a bit of a knowledge of color psychology i.e. the effect of colors on a person's mood helps in an appropriate selection too. In addition to this, the maintenance and up-keep that some colors require is also an important criteria to be considered.
Ideas To Consider
A creative idea is to paint the walls in green and the ceiling in blue. On the ceiling, you can paint a few white stars with the help of stencils as well as some scattered clouds.
Paint the walls in any light color of your choice. Next, create an accent wall, by painting some designs in bright colors like red and orange on it.
A Creative Touch
These days you will find chalkboard paints in the market, which create a "blackboard" on the walls. So you can consider painting a portion of the wall with it.
An interesting idea is to paint some "games" on the wall and the floor. You can create a hopscotch game on one of the floor corners and a dartboard on the walls. The kids will love playing these in their spare time.
Creating textures on the wall by using techniques like "sponging" will give it a unique look. You can consider painting some of the things that your child likes on the walls to make them interesting for him, such as airplanes, cars, butterflies, flowers, fairies, mountains, oceans, and the like.