The beaches in Marmaris Downtown are not the greatest in the world, but are more than adequate for children and adults alike. The sand is mostly black sand and a bit gritty.
The beaches are not very wide and the top half is covered in sunbeds and umbrellas which you can rent for a nominal fee if the hotel/restaurant does not provide them. Many hotels have private beaches, and some even ship in very good sand from other areas. The sea is warm, crystal clear and perfect for swimming.
There are some fabulous beaches within half an hour’s drive, so if beaches are your thing.