The Heian kata, originally known as Pinan kata, were developed by Anko Itosu from old Okinawan kata, particularly Kanku Dai (Kushanku), for teaching high school and university students karate forms. During the transitional period of Gichin Funakoshi introducing karate to mainland Japan, he renamed the kata to Heian. Both Pinan and Heian kata loosely translate to "peace and calmness" or "peace and harmony".
Itosu introduced the Heian kata into the school systems of Okinawa during the 1900’s and they still form part of the curriculum in many styles today. The Heian kata consist of five separate kata and are the building blocks of more advanced kata in the school systems. It is usually because of this reason that many practitioners regard the Heian kata as merely gym or preparatory kata and not a fighting system within itself. Some even believe that the Heian kata were developed solely for children.
Perhaps another view could be although the Heian kata served to bring karate into the schools and universities of mainland Japan, the very roots of their origin would indicate that Itosu developed the Pinan/Heian kata as an effective fighting system and the methods and bunkai passed to him from his ancestral teachers formed the foundations for these kata. So rather than interpreting the Heian kata to be basic exercises to prepare Karateka for more advanced kata, they could well be the building blocks for effective bunkai, methods and principles. Like all kata, the key is to study to gain an understanding of the principles and methods behind the kata.