The Mid-size SUV will probably be a Ford Explorer which seats 5 people so you will have an adult and 2 kids in the back (will the kids need car seats?) and an adult in the front, and then your luggage will have to fit behind the back seat. It will probably be tight and I would definitely go for the full-size, just to make it comfortable. My husband and I used the mid-size SUV and we had (2) large backpacks and (3) rolling carry-size bags which took up a lot of the trunk floor. There was more room to stack luggage, but again, there was just 2 of us, so a family would require more space.