One of the prompts in the Autumn Challenges which ended last month was all about a witch's or wizard's New Beginnings, that is, we should show how everything went when they first got their letter. I used Colin Creevey, and he and Dennis were able to see The Leaky Cauldron though their parents did not until they led their parents to and inside it. There are quite several other Muggleborn-centric entries, too, I think the categories are still there, maybe you can have a look at them to see what others did.
I imagine the Leaky Cauldron is the link between the Muggle and Wizarding worlds. Think about it, Britons are fairly used to pubs. The Leaky like the antechamber into the wonders of Diagon Alley, which is open to Muggleborns' parents and guardians because a child can't very well shop alone. Moreover, Diagon Alley is the ideal place to introduce and show the magical world to the Muggle parents/guardians, everything is there, after all.
And then the Platform, Mr and Mrs Evans got through, didn't they? So I'll agree that the Muggle repelling charms are probably nulled, when, say, a witch or wizard is holding on to the Muggle and leading them to the platform. Of course, perhaps telling them that they can get through is enough to null the charm, if they believe it. Of course, they'll believe it when they see their daughter doing it.
These are my thoughts, I hope I helped, too, Ana.