In a kids' bathroom, the emphasis is rarely on creating a feeling of tranquility – it's a great place to get playful with bold, bright colors and contrasts. The main goal is to keep the space feeling bright, clean and fun. There are lots of ways to accomplish that. You can either stick with a white backdrop – white walls, floors and fixtures – and bring in color with the shower curtain, bath mat and towels, or jump in with color on the walls that accentuates the room's other elements.
The first approach will give you a little more versatility if you want to be able to quickly update the room later, since nearly all kids' bathroom linen collections are going to look great with white. To pick a color for the walls, it's a good idea to choose the shower curtain and towel collections first, and then use one of their colors – or a tonal variation of one – to guide your paint or wall covering. If you or your kids are particularly drawn to a strong or deep color that you don't want to apply to all the walls, consider using it on just the trim, or using a stencil to create a colorful pattern.
Blue and green are popular starting points for bathroom palettes, since they evoke feelings of cool water. But yellow and orange can bring a fresh, sunny feeling to the room that kids will love, and reds and purples will bring an unexpected pop of energy. Don't forget that if you've chosen a shower curtain and bath mat with bright colors in them, you can use a lighter tint of one color to add interest to the walls without overpowering the room.