I've looked inot this and came to the conclusion that the army style stong hoop on the bulkhead is a good solution. It roll over protection not a roll cage. Roll cages really need to go through the tub onto the chassis and its a lot more modification and (as above) only make sense with a full harness otherwise the roll cage injures you not the bodywork. I also drive with 1 child and have made a few mods: 1 drive sensibley and defensively. 2 cover sharp edges, I have roll cage protection on the door pillars, 3 sort out the seatbelt mountings and fit backing (pull though) plates. 4 Fit a dog screen when there is load in the back, including backs and camping junk - (I was nearly decapited by a flat pack wardrobe - lesson learned!) 5 fit more lights, especially high on the rear, it seems series are invisible on motorways.6 Make the seat fixings work properly - the straps on the seat back etc, you don't want everything flying about.
On the lights issue, I have small very bright LEDs, about 3/4" dia that can be seem at about twice the distance of the std rear lights. Easy to make some brackets up. I was at a military rally recently and a guy in a Jeeep came up to me and asked about them, it was bad weather and he said my vehicle was a lot more visible than the others, they had just come back from a trip to Dunkirk and a WW2 Jeep had been rear-ended while drving at 50 mph by a driver who "didn't seem them", it was a bad accident.