First you will need to strip down the room & assess the drywall situation… you’ll need to fix up any holes before you paint (you have boys you know there will be holes!) this will give you a quick DYI fix. Once this is done it’s time to move onto the painting.
Here’s a guide to picking the right kind of paint. as for color well I would go with green of some sort just to be a purist. However I have seen some amazing Brick Wall Decals so you might want to make an accent wall with brick & add a few ninja turtles right on top of that. The look will be insanely cool. I’d do this on the wall with the bed.