My son (now 17) has had his little Oztrail 3man tent for about 8 years now and so far so good. He takes it on longer trips and camps in it rather than with his two sisters in our CT.
He has a king single swag which is a little too long for the tent (he doesn't like his bedding touching the walls when its wet) so he puts it across ways and has room for all his other stuff (ipod, portable dvd, guitar, bag etc) in there as well
This is what it looks like: but his is blue with a silver fly & was pretty cheap to buy.http://www.oztrail.com.au/dome-tent-range/classic-tent-series/DTC-3P-C.php
It has been through a hell of a lot of punishment and quite a few storms over the past 8 years or so and stayed up and kept everyone dry. His sister's and their friends have also given it a run for it's money using it for backyard campovers!!
It has kept them dry and warm also but does tend to get quite hot in the middle of summer, but tarp over the top will fix this. All of the kids can put it up on their own so that is a definate plus.
Had not one issue with it, all the zippers, fly and poles are still in mint condition.
But I would go the next size up to fit both kids in there with their king single mattresses.
Hope this helps