I think the point of separating the children from mage parents is to avoid any sort of dynasty within the Circle, no inheritance issues if separated. Maybe.
Still, Bethany in Kirkwall was able to send letters, so it's not like communication is cut off. Finn from Witch Hunt even got gifts from his parents and speaks of them often, so they have a good relationship. He was even allowed to adventure with the Warden with only a, "Okay, sure, but be careful" from the Templars. What?! Then again, it was Fereldan, where a Circle mage was also able to have a house and family with no one raising a stink about it.
Probably varies from Circle to Circle. Pattern seems to be: don't rock the boat, get more freedom to do whatever.