How can I paint railroad ties that are currently being used in an outdoor playground?

I would like to paint them a bright color as they are currently dull brown. Our grade school playground needs some bright colors and thought this would be an inexpensive way to help.How can I paint railroad ties that are currently being used in an outdoor playground?
I wouldn't paint them! Lumber like this is pretreated to repel water and mildew and won't take a paint well, even if you prime it. If it's older timber, chances are it's emitting carcinogenic matter. Best just to leave it alone.





If you'd really like to brighten things up, how about adding trees/flowers around the edges to the space? You can usually get a discount from local nurseries and the kids could help plant. This may be something your PTA would be interested in sponsoring because you can also turn it into a neighborhood plant sale. We used to do this every year with great success.