I wouldn't do anything too extreme or permanent, like paint a giant zoo mural or anything. Paint the walls with a good SCRUBBABLE paint that won't show dirt. Choose a sturdy floor-covering. One of the best things we ever did, honestly, was to take up the carpet out of our tomboy-daughter's room and replace it with vinyl planking: MUCH easier to care for than carpet! Don't put anything that is delicate, rare, or requires specialized care in a young child's bedroom. Once you have a good, basic room, you can decorate all you want with linens, lamps, curtains, pictures, rugs, etc. Your child will probably not really remember what his room looked like when he was a toddler, and later, when he displays some type of interest, you can buy a new coverlet and curtains and change the room to suit him more.