If you ever went camping with kids, you know already that a family of four needs more space than a group of four adults. This happens because families usually need more gear, including air mattresses, toys, more clothes, and sometimes even small appliances. With this in mind, you should get a tent twice the size of your party.
For instance, if you are two adults and two kids, you need an 8-person tent to camp comfortably. A 6-person tent could do too, but you may have to squeeze, especially if you have lots of gear. Sure, a smaller tent could save you some bucks if you’re car camping and don’t plan to keep all your stuff in the tent.
Thus, the rule of thumb is to consider a capacity of at least two more people larger than the actual size of your family.