How involved are Muggle parents in the school lives of their magical kids?

Question

Two parts:

• Are parents in general permitted to make visits? If yes, does this include Muggle parents?
• If, for any reason, a Muggle family intends to move house and relocate, are they allowed to withdraw their kids from magical school? This is probably irrelevant if they're still living in the same country, but what if they move abroad, nearer to a different magical school?

Answer 1

1. It's not explicitely stated, but parents (Muggle or not) don't seem to be able to make visits to Hogwarts in general. The only parents (or siblings that already left the school) we see are :
   • when their child is injured and they come to visit at the hospital wing - and only if the injure is really bad
   • the champion's families are allowed to come and support them for the third Task of the Triwizard tornament

     "I'm aware of that, Potter," she said. "The champions' families are invited to watch the final task, you know. This is simply a chance for you to greet them."
     (Goblet of fire, Chapter 31, The third task)

   • when they come to take their kid home in emergency (the Patils, Mrs. Finningan and some others removed (or tried to) their kid after DeathEaters came and fought in the castle and Dumbledore was killed.

     Some students were hurried away from Hogwarts by their parents over the next couple of days - the Patil twins were gone before breakfast on the morning following Dumbledore's death and Zacharias Smith was escorted from the castle by his haughty-looking father. Seamus Finnigan, on the other hand, refused point- blank to accompany his mother home.
     (Half Blood Prince, Chapter 30, the White Tomb)

All those are quite exceptional! So I don't think parents visits are really authorized, unless it's necessary (once again, Muggles as well as wizards parents).

I guess Dumbledore wouldn't forbid Muggle parents to come and visit their injured kid, but since Muggle cannot really come near Hogwarts, I'm not sure it would be possible. Maybe they could come close to it, then a teacher would go meet them, and acompany them to the castle (performing the needed actions to let the enchantments make an exception, like Dumbledore did when he and Harry flied back to the castle when coming back from the Locket Cave). (This is just my guess)

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EDIT (thanks to Janus Bahs Jacquet's comment)
It's indeed possible for Muggle parents to come in Hogwarts:
Moaning Myrtle has Muggle parents, since Draco calls her a Mudblood:

But I know one thing - last time the Chamber of Secrets was opened, a Mudblood died.
(Chamber of Secrets, Chapter 12, The Polyjuice Potion)

And they've come to Hogwarts after her death:

"The dead girl's parents will be here tomorrow"
(Chamber of Secrets, Chapter 13, The Very Secret Diary)

--

(I don't count relatives that come "on duty", like Percy to represent the Minister, Charlie who took part to the first Task organization, or Lucius Malfoy who's on Hogwart's board - cause they'd been there even without having a son/brother at the school).

2. For the second question, I think the question is the same whether the family is Muggle or not : a wizard family moving to France might also wonder if they should send their kid to Beauxbatons. I don't believe there is any canon answer, but we've got some clues:
   • It seems to be possible to send a kid to another school, since Draco said his father had thought to send him to Durmstang. I only write "seems", cause it was Draco, we cannot be sure he wasn't boasting.

     Father actually considered sending me to Durmstrang rather than Hogwarts, you know. (Goblet of fire, Chapter 11, Aboard the Hogwarts Express)

   • Allowed or not, it's possible for parents to take their kid from the school : like said earlier, some parents did this, at least after Dumbledore's death. (And maybe also after the attacks in the Chamber of secrets...)

So probably it's possible for parents (wizard or Muggles) to decide that their children should attend another school.

-- 2nd EDIT: I'm (re)^n - reading them, and just found this, confirming that parents can send their kids abroad, or even keep them at home (Lupin's speaking about new laws decided by Voldemort once he ruled the Ministry):

“Attendance is now compulsory for every young witch and wizard,” he replied. “That was announced yesterday. It’s a change, because it was never obligatory before. Of course, nearly every witch and wizard in Britain has been educated at Hogwarts, but their parents had the right to teach them at home or send them abroad if they preferred.
(Deathly Hallows, Chapter 11, The Bribe)

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But I'm not sure that a family moving abroad would decide this : after all, the children still are British and english speakers (they don't seem to learn any foreign language), why should they go to another school, potentially with lessons in another language?