Now (about F2B & F3 kinds of family-based immigration):
If American citizens or permanent resident has handled family-based immigration for their adult children (over 18 years old) in before, their adult children must be unmarried, when the waiting period will reach, their adult children can go to USA, and can be got the temporary resident status, they must go to work, or go to school, prohibit to stay in USA but do nothing. They can't be got U.S. permanent resident status.
About if citizens or permanent residents has handled immigrant for their minor children, but now their children have been over 18 years of age. And American citizens or permanent residents have handled immigrant for their adult children.
They must fulfill these:
They must go to work or go to school in USA.