Safe, inexpensive family car for 5

The Toyota Highlander would be the best option on your list because it will run for a very long time if it is taken care of. However, the Toyota Sienna is just as reliable and has a lot more space. I would totally go for the Sienna over the Highlander if I had five kids. You don't want to put three kids in car seats in the second or third row of a Highlander. All cars will be similarly safe and efficient. The minivans and Volvo would be expected to fare better in a crash.

If you really want efficiency, the Highlander Hybrid is available, but don't get one too old because the batteries age with time, not mileage. I wouldn't recommend this option as this hybrid system was a little less efficient than the Prius at the time, even considering the large size of the Highlander.

LectroFuel is assuming you want a 7 passenger car even though you listed two 5 passenger models (Volvo & Subaru). Actually, w 3 kids, a 7 passenger rig makes a lot of sense, especially if you plan to keep it a long time. He knows his cars and is right on about the Toyotas for a 7 passenger model.
But back to to the 5 passenger models.
Volvo XC 90 is nice alright but will have a higher initial cost and higher maintenence cost than an Outback. If your OK with a 5 seater, a Subaru would be the way to go. You might also consider the Subie Forester. It isn't quite as cushy as the OB, but has a similar amount of room, equipment, and some prefer it -- may also be a couple thousand less for similarly equipped Outback. Many Subie owners put well over 100,000 miles on there without major repairs although about 10% (more if earlier than 2015) use oil, major engine failure is very rare.
Disclosure: I have owned 1 Forester and 2 Outbacks with very little problem (but never kept one beyond 75,000 miles).
Good luck and please let us know what you decide on.