your only real limitation here is 3 car-seats side by side.
(truly 2 car seats and a booster depending on how large your 5 year old is - remember safety for kids isn't about their age, it's about their height. They need to be large enough for the safety systems to work whether that's a seat, booster, or belt). I envision the infant seat in the middle, and the larger car seat and booster flanking.
Truth is most van's wont work for you because they have captains chairs so only have 2 seats anyway.
In terms of most compact Scion Xb would work but they don't make them anymore
You really would need to go to a dealer with your specific seats and test it in the specific car because your actual seats may not work whereas another brand may. It's unfortunately a process of elimination.
I remember when I was shopping after our first, we took the jogging stroller to the car show to see how many trunks it fit in. Believe it or not it wouldn't fit in most SUV trunks but fit in most sedan trunks easily (because SUV trunks are very shallow from rear seat to hatch and it couldn't lay down, sedans are deep and it just plopped right in).
But to specifics, you can try any of the BMW X mobiles as they are the better driving SUV's out there. Believe it or not I felt the X1 had a fantastic back seat, especially for kids. It's more than spacious for two, but it may not do well with 3. Of course any 3 row works because the 5 year old goes in the way back. So that gives you Mazda too in the CX-9. (there are other 'tweener' SUV's like the atlas, ascent, telluride, and pallisades, but none are drivers cars like the Mazda is).
But in 2 rows, the Hyundai Santa Fe sits 3 across, not sure if it's 'fun' most hyundai's are on the softer side by design. Also the Honda Passport (the 2 row 'fun' version of the Pilot).
In terms of sedans, you've got the Avalon, it's a boat, but they make a TRD version.
here's an older list:
https://www.cars.com/articles/which-...1420668847322/
the European cars don't do well in this test because they are not wide on the inside. Volvo has great built in car seats and boosters but they really only fit 2 in the rear.
I happen to like that the charger makes the list because I thought it (and the challenger) were lots of fun. Truly huge rear seat too.
Only downside is the windows are small. For kids, I like the largest windows possible so they have the most light, feel the most space, and have from what to look at so they aren't bored and most importantly don't get car-sick. (Subaru does really well here).
Seth