Renting a 4 wheel drive car
 

Does it matter what 4 wheel drive car we rent? Each 4x4 has the amount of cc's next to them. For example, 1300cc, 2000cc etc. I was looking at the Daihatsu Terios car with 1300 cc's.
We are going to arenal, monteverde, playa flamingo and Manuel Antonio. Also, is it better to rent a car by the airport or in San Jose.

Just make sure you get a 4 x 4 SUV, just getting back from 2 weeks travel to 5 different regions, we watched the cars having a very hard time on the roads. We had a Jeep Wrangler from Thrifty and had were happy, but it is a bumpy ride on those roads! We rode in a Terios for one of our tours and it seemed to handle the roads well too.

We rented Terios from Toyota rent a car next to SJO. They are considered to be off the airport therefore there is no airport surcharge. We had it for 2 weeks and drove to Arenal, Montaverde, Playa Grande, Manuel Antonio. The car handled fine. The engine is small but with only two of us it was enough. I could see possible problems if you have 4 large people in it driving up the mountains.
For some reason renting it through Ace car rent (affiliated with Toyota rentacar) was cheaper for the same vehicle. I have no idea why was that.
Make sure to check your tires no matter where you rent from. Bald and/repaired tires are common.

We are 2 adults and 2 kids (10 and 15 years old). So renting a Daihatsu Terios should be fine especially going from Arenal to Monteverde?

I think you will do fine power wise in the Terios. However, if your kids are tall (long legs) then it might be not as comfy in the back seat. I am not sure how back seat space room is in RAV4 but it’s probably roomier than in Terios.
Most of the car rental places don’t require prepayment (Ace certainly didn’t in our case), so what you can do is to make reservations for Terios and just in case for a bigger 4x4. I know people might think it’s not nice, but you got to do what’s best for you. It’s not like you can go to a car dealership in US and try to sit in Terios.

We had two adults and two kids and rented a Suzuki Gran Vitara. We fit okay, but there wasn't a lot of room for the luggage. It was a tight fit! I think the Terios is even smaller.