Arosa: CHF 7.80 per person per night. Visitors under 12 years receive a 50% reduction, i.e. CHF 3.90 per person per night.
No full exemptions are stated. Visitors under 12 years receive a 50% reduction.
The source provides no specific rule for short-term, Airbnb-style rentals, no cap on nights, and no separate rental exemption or rate. It only states that the tax applies to all visitors.