General terms:
* Mild
* Temperate
* Soft
* Gentle
* Moderate
* Subdued
* Soothing
* Calm
* Peaceful
More specific terms:
* Lenient (referring to punishment or rules)
* Forgiving
* Tolerant
* Compassionate (referring to empathy and kindness)
* Discreet (referring to behavior or speech)
The best word for you will depend on the specific context.