Hi,
I know someone who traveled with a family of 6 and in a regular cab truck that only seats 3. So the rest where in the trailer. His wife, and kids. They had a intercom to the trailer, and it was legal. Safe? Well - some states say it is legal to allow people in a fifth wheel while driving down the road. Many states will not allow anyone in any trailer on the freeway or any other highway. I don't think any state allows passengers in a travel trailer. Some states are even making it illegal to have passengers in a cabover camper on the roads.
Try looking at a class C motorhome, where the kids will be a lot safer, and walking to the bathroom is not a problem. They can watch TV on the overhead TV set, watch a DVD or something. Use a 12- 120 VAC inverter to run the TV while driving. Many have seatbelts for as many as 6 passengers.
Have fun camping!
Fred.