I think Psi Corp has a tricky line to walk. They have to look like the good guys, after all. Normal mundanes, ones who don't know about reeducation camps and psi experiments, think it's there to keep the telepaths in line and make life better.
To that end: I suspect they would have some rules in place that don't allow non-Corp on the campus, and then never allow the children off campus. I suspect they never outright forbid it, but a lot of pressure can be applied by adults when children are concerned. There are no paper trails where a parent can say "They forbade my child from seeing me", but the kids probably don't go home. And after a few years, they don't want to. Or they run, and become blips.
Also bear in mind that there is instantaneous video conferencing available everywhere. If you're limited to email, well that's tough, but if you can call mom and dad and see them...that probably lessens the sting for the first few months. Then you get busy, then you forget to call...
Finally there's the obvious point: it's possible they simply subtly reprogram the kids to not want to go home. Remember Talia's account of her first handler? She said she was being scanned and felt really warm and accepted and comforted. It's possible a few subtle things are implanted early on to keep the children more loyal. That's never stated, and the Corp seems to prefer traditional methods of brain washing on their own, but who knows.