After much research, we bought a new tent. It's a Kelty Trail Dome 6 and we got it off Amazon.com. I'm excited to put it to use later this month in West-Central MN. It will be so much nicer than the 3-person tent we've used for years - before we had kids.
One thing we learned when researching, a 4-person tent is really best for 2-3 people and a 6 person tent is ideal for 4 people. So, we went with a 6-person tent. We found the following illustration of how 6 people would sleep in a particular model - which cracks me up. Who would sleep like this?!