In "R-1", "R-2" and "R-3" Districts, any place, home or institution which receives six (6) or more children under the age of sixteen (16) and not of common parentage, for care apart from their natural parents, legal guardians or custodians, when received for regular periods of time for compensation; provided however, that this definition shall not include public or private schools organized, operated or approved under the laws of this State, custody of children fixed by a court of competent jurisdiction, children related by blood or marriage within the third degree of the custodial person or to churches or other religious or public institutions caring for children within institutional buildings. The term "child or day care center" shall be deemed to include nursery schools and private kindergartens or preschool facilities.