After 18, get a job and pay rent, go to school or get a job and move out. you are hurting your children if you do otherwise.
I feel exactly the opposite. Placing an unreasonable financial burden on your children too early in life can keep them poor for the rest of their lives. It can ruin their lives.
I had friends who over-borrowed to go to college and get their degrees and live on their own while doing so, even while working 2-3 jobs at the same time, while their parents claimed that they were "teaching" them to be self-sufficient, and now they're still paying off college loan payments that cost 50% more than TheBoyfriend's mortgage and have never bought a house even though they're in their mid-thirties!
In the Asian community, it's exactly the opposite. Parents encourage their children to remain as debt free as possible and live at home until they leave school, or even until marriage and work and save their money. They're ready to buy a home in their early twenties. When they reach their mid-thirties, they're much more stable financially.
I've seen the results of both philosophies with my own friends. I have to say that the parents who kicked their kids out at 18 were stupid, considering where their kids ended up 20 years later.