On a beach holiday, my son has stitches on his knee after falling. the dr said he must keep it dry but can do everything else. is that correct?

Correct: Don't want to get it contaminated with dirty water from the ocean or lake you are at. Worse would be a public swimming pool. I tell my patients they might as well put their wound in the toilet. I would also recommend he not get it sunburned as it is more likely to scar. He can usually bathe with it unless your doctor specifically said not to.

Sounds like : Good advice. Keep clean , dry and watch for signs of infection.