Pups are occasionally left by their mothers for short times and this is perfectly normal. The pup may also cry whilst it is left which may sound distressing to you but they are perfectly fine. The most important thing to remember is to always keep your distance and not approach any seals as this can cause unnecessary stress.
Up until the pups are three weeks of age they are covered in white downy fur. During this time they are not ready to swim so please do not try to encourage them back into the water.