[wizzwizz4]

If they can cope with / get used to the intense new sensory input, I imagine the same tricks would work (point out interesting things, make sure they understand what's going on so they know what to expect (but without making it an ominous future event), etc). That might require making the hairdressers' quieter or less crowded, though. (Timing your first time well is probably important; I'd aim for somebody else to watch first, but not large crowds, but it depends on the child.)