It's common in spring and summer to find young birds sitting on the ground or hopping about without any sign of their parents.
This is perfectly normal, so there's no need to be worried. These fledglings are doing exactly what nature intended, and left the nest deliberately a short while before they are able to fly.
If the bird is on a busy path or road, or other potentially dangerous, exposed location, it makes sense to pick it up and move it a short distance to a safer place. Make sure you leave it within hearing distance of where it was found. Birds have a poor sense of smell so handling a young bird does not cause its parents to abandon it.
If a healthy chick cannot be returned to its nest, it will be dependent on humans for survival, and should be passed on to an expert rehabilitator as soon as possible.