When Harry meets the Malfoys at the platform in fanfic, it's a situation full of potential drama. Harry's Gryffindor nature would clash with the Malfoys' Slytherin ways. Draco might start a verbal sparring match with Harry right away. Harry would be aware of the Malfoys' association with Voldemort and be on guard. The Malfoys might try to undermine Harry's confidence, but Harry has his friends and his own strength. There could also be a moment where Harry realizes that there is more to the Malfoys than he initially thought, perhaps seeing a glimmer of humanity in Narcissa or a sign of hesitation in Lucius.
Well, it could go a few ways. One possibility is that the Malfoys would start their typical taunting of Harry. Lucius might look down on Harry with disdain and make some veiled threats. Narcissa, on the other hand, could be a bit more reserved. Harry, being Harry, would likely respond with his own brand of courage. He might even try to use the situation to gain some information about the Malfoys' recent activities if he suspected they were up to no good.