For many folks all the little birds running around on the beach are sandpipers and although that is not always technically correct it is often close enough. Even good birders refer to the whole group as "peeps" or "pipers" and sometimes indentifying them, especially in winter can be tricky.I took this photo at quite a distance but I believe these are sanderlings in the top picture. The area I took the photos in has had both dunlins and western sandpipers over the last few weeks as well as sanderlings and winter shorebird plumages can be a tough call. You need to look at the overall shape, size, behavior, etc.
I believe the bird in the second photo is also a sanderling. I thought it might be a dulin, which are a bit chunkier and have a longer bill that curves down a bit but another birder I spoke with is pretty sure it is a sanderling. I am happy to be corrected so please feel free to chime in.
These two shots are definitely of sanderlings. Jaunty little guys, don't you think?
They are often on our beaches all winter and will soon be molting and getting their summer plumages. The dunlins will, too. Then they will all be off to the north where they will mate and nest. They will return here in the fall.