I had my Model S P85+ for over 3 years. In the beginning the rear jump seats were really cool. But the novelty soon wore off as there were clearly put in as an afterthought. There is no ventilation in the rear. So in the summer heat it is really bad. We rarely use the rear jump seats because of this omission of cooling.
But in a pinch and when you really need to carry up to 5 adults and 2 kids, then you can use the rear jump seats for any short 20 minute trips. Anything longer you will need to buy some kind of cooling back there for the kids.
Restrictions for the seats per the manual are:
“The Tesla built-in rear facing child seats are child restraint systems and must only be used for children over 37″ (94 cm) tall and weighing between 35 and 77 lbs (16.2 to 35.2 kg).”
I bought two things for them when they sit in the back. A misting fan and also a battery operated bigger fan.
Links are below:
Automotive Dual power fan