Question
we have three coastal redwood trees- about 25 years old - in our yard. The roots are beginning to protrude above the lawn surface and present a hazard to children playing on the lawn.  Any suggestions?

Answer
You can add sand over the roots as long as it does not cover the roots by more than a couple of inches deep. This will make a smooth surface but over the years the roots will continue to grow and be exposed so you will need to repeat when this becomes a problem again. Redwood tree roots grow shallow in the soil so you can expect some to grow above or at ground level.