I've never said that. I can just imagine them saying "Fine! I won't live here then" and they would run away.
They've got some place lined up to go? I know I certainly didn't at that age, laugh
. Anyway, they don't need your permission to run away, they could just pack their bags and do it; and many children do, if they really don't like their home situation. Frankly, though if your children want to run away.. I'm sorry, but I would seriously question your parenting skills. I went so far as to tell my parents I would spit on their graves and I had a few physical fights with my dad (just a few), but I only once contemplated running away, when I turned 17. I think my mom was fairly wise, though, because she arranged for me to go live with someone she knew for a while instead. She felt that being out of the home would be good for me and I think she was right. She kicked me out for good when I was 21 (she knew I would go to live with my dad, who separated with her at that time). She still helps me out a bit, but that's the last time I actually lived with her. They were somewhat more protective of my younger sister, but she managed to have sex at 13 anyway. She apparently regretted it, but I'm almost sure nothing came of it (pregnancy, stds). She may well have used protection, but I have never asked..
I hate conflict and if my children were so eager to leave my place and had the means to do it (and I felt reasonably sure that the person they were going with wasn't a bad person), I would much rather give them wings then have them doing the equivalent of making that icky chalk scraping sound on a blackboard.
Both my parents essentially left home before hitting adulthood. My mother went off to study at a boarding school and my father went off as well (I think he may have gone to live with a girlfriend, but he continued to study).