I read it about 1992.
A human colony exists on a very hot planet. There are benevolent aliens that shed their head and hands as part of their life cycle.
The kids want to grow up faster so they decapitate one of their group and get sent to various prisons.
The story picks up many years later when they are adults. More details:
- I believe the humans have to use VERY thick sunscreen on the planet.
- One of the girls becomes a sex slave to aquatic aliens.