Cover a table or flat surface with newspaper.
Remove all of the guitar's accessories, including the strings and tuning pegs.
Cover the guitar's fretboard and sound hole with duct tape or masking tape.
Place the guitar on the newspaper-covered surface.
Sand the entire wood surface of the guitar with 100 grit sanding paper until smooth.
Wipe off all dust, and clean the surface of the guitar with a damp cotton cloth.
Wear a paint mask to avoid inhaling fumes.
Apply a primer, either in spray-on or paint form, to the body of the guitar. Let it sit for 24 hours.
Sand the body of the guitar again to remove any imperfections left behind by the primer.
Spray paint one side of the guitar, creating the design of your choice. Guitars for kids games often include an array of colors, and fun designs such as stripes and polka dots. Allow it to sit and dry for 24 hours.
Paint the other side of the guitar. Let it dry for 24 hours.
Apply any decals or added design elements to the guitar. Decals featuring music notes are a popular choice for kids.
Remove all tape from the guitar's surface.
Reassemble the guitar, restringing it and screwing the pegs back in.