Adoption of children may be refused on the grounds of the unsuitability of the applicant foster parents with regard to age, religion, or criminal record. Natural parents may refuse to let their children be adopted without the possibility of reclaiming them. A minimum age for foster parents may be stipulated by the law and a required difference between the ages of the foster parents and child laid down (as in the UK and in France). Single adults are usually considered unacceptable (but not in France).