How long can kid be in foster homes?

Until they reach the age of majority. In other Words, unfortunately, a child may never be adopted and will remain in state's custody until he or she reaches adulthood.

This answer of course relates to a child whose parents have had their parental rights permanently terminated by the court either voluntarily or otherwise.

This is an incorrect answer. If a minor child's parental rights have been terminated, they can be adopted. The adoptive family can be the Foster Parents, other family members or an unrealated family. My husband and I are currently in the process of adopting an 8 year old girl who is currently living in Foster Care System.