Cedar is used for playsets and play structures because it is resistant to pests and is low maintenance. Sealing or staining cedar is not necessary, but it naturally weathers to a gray color if left untreated. This is normal and it does not change the playset's strength or durability. However, if you want to sustain the new look of cedar, seal the playset with a waterproofing stain.
For this job, you will need a waterproofing stain in a clear or semi-transparent color. You want the natural look of cedar to show through, so choose a cedar semi-transparent color or a clear stain if possible. Since the playset is for children, choose a non-toxic and low VOC, which stands for volatile organic compounds. It's better to be safe with a children's play structure. You will also need brushes, newspaper or rags, flathead screwdriver and paint stirrer.
Remove any peeling stains or paints from the playset with sandpaper if necessary. Spray the play structure with a garden hose to clean off any debris on the wood. If it is very dirty, use a mild soap to clean. Allow it to dry completely for 48 hours before staining. Most stains need to be stirred and it is best to have the hardware store mechanically shake the container for you. If not, use a paint stirrer to stir the stain in the container. Lay rags or newspaper underneath the container and use a tarp on the grass around the play structure if you do not want stain to spill onto it.
Start this job late morning or early evening. It is best to stain the play structure when it is in shade and between 50 to 95 degrees Fahrenheit. Brush on a small test area to be sure the stain is the right color or transparency. Dip the top 1/3 of your brush into the stain's container and brush on the stain evenly all over the wood of the playset. Work from the top to the bottom and brush on one coat.
Allow the playset to dry for 24 hours. Some stains need only soap and water for cleaning up brushes, but other stains recommend paint thinner to clean the brushes. Most stains recommend re-staining after about one year because of the heavy wear of children playing on the set. It is best to purchase new stain the following year and dispose of the leftover stain at a garbage facility that accepts hazardous waste.