In order to clean a urine-soaked mattress, first soak up the urine, then use cleaners and dry the mattress. These steps for cleaning a urine-soaked mattress are outlined on the Fisher-Price company website.
If the stain is new and wet, use a dry towel with pressure to soak up the excess urine. The pressure can be applied by having a heavy person stand on the towel that is placed on the mattress. Blot with new dry towels until the liquid is absorbed; this can take about an hour. If one is available, a wet-dry vacuum may be used, instead.
If the urine-stain is dry, apply 3 percent hydrogen peroxide on the mattress, and leave it there for 5 minutes. Be aware, however, that peroxide may bleach the mattress. Dish detergent, vinegar or borax can also be used to clean urine stains. Blot with dry towels once again to soak up the moisture.
Next, apply baking soda to the stain, rubbing gently with a soft brush or firm sponge. Leave the baking soda on overnight then vacuum off the dry powder the following day. If possible, put the mattress out in the sun during the day, or use a fan or hair dryer to expedite drying. When the mattress is completely dry, flip the mattress over and use the clean side to sleep on.