It is a tin can....
Of course all cars are tin cans.
Compared to a modern car, an X is not very safe. Compared to the majority of cars from its era, it is very safe. The biggest issue I would have with an X is how low it is and how tall all the SUVs and pickups are, being driven OVER by a much heavier car that bypasses safety structures is not a nice idea.
Unless the late Xs in Europe went through NCAP, there is likely little or no crash data on the X. You might look in AutoZeitung, they used to crash all manner of basic vehicles, they may have crashed an X.
I drove around with my then new born son in the front seat of my X for the first year of his life and never felt particularly worried about it.
To satisfy your ex I would drive your child to and fro in another vehicle, giving an ex more fodder to needle you with is a zero sum game. With gas back down around 2 bucks how much are you really saving.
There is a really illuminating Mythbusters where an X was sacrificed between two semi's that smooshed the X between them. The X did very very well give the energy involved. I will try to find a link.
Its enough to make you cry...
http://www.asemblr.com/player.php?id=770
mythbusters: Compact Compact The Vodka Myths episode 41 Season 3
Episode 41: Compact Compact and Vodka Myths
Two semis trucks can collide, fuse together on impact, and hide a small car between them: mythbusted
Vodka Myths:
Vodka as foot wash: confirmed
Vodka as mouthwash: confirmed
Compact Compact:
Myth: Two semi-trucks are in a head-on collision and get fused together. Awhile later in the junkyard people start to notice a smell coming from the trucks. They pull them apart and find that there was a small European car wedged between them with a dead driver. In a variation of this myth the two trucks were tailgating.
Test setup
Ingredients:
two free cab-over-engine semis that they got for free
two tow trucks
one small European car (donated by fan Jack Friedman)
3/8" cable (20,000lb breaking strength)
pulleys
long strench of open pavement (same as used for Matrix: Reloaded)
5000lb steel plates to weight down each semi's trailer (to simulate full load)
Buster ('driver' for the car)
Simulaids ('drivers' for the semis)
Instead of driving the semis into each other, they decided to use tow cables to pull the semis into each other so that they could get a simultaneous impact. Guidebars were welded to the front of each semi so that they would steer with the cable.
They marked off a T-shaped course with 1500 ft of road in each direction from the collision point. The semis were lined up at each end of the horizontal and attached to the tow cable. Two tow trucks were lined up on the vertical to pull the cables and the small European car was stationed at the intersection. The tow cables were run through pulleys bolted to the pavement underneath the car out to the semis. Ropes were used to attached the tow cables to the tow trucks to breakaway when the semis collided.
Test run
In their test runs for the tow lines the tow rope snapped, sending one of the semis on a runway course into a field as the MythBusters crew went running.
Adam: "I have no idea what your plan was for stopping it"
Tory: "Yeah, there wasn't really a plan"
Jamie: "In this case we saw what we wanted. We narrowly had a little bit of a disaster as far as automobiles getting crunched by a runaway semi-trailer truck, but, you know, details"
Test 1
Jamie: "The second truck is out of control I believe, over"
A tow cable snapped causing one the trucks broke free and roll off into the grass. The other truck stayed on course, slamming into the car and using it as a brake. They pinned the failure on the fact that the tow trucks weren't keeping pace with one another. As the other tried to accelerate to match it may have snapped the cable too hard or caused the truck to run over it's own cable.
They managed to repair a busted guidebar, bent-up pulley system, and cable in 90 minutes so that they could give it another shot. Although the car was damaged, they figured that it was still intact enough for another shot.
Test 2
Jamie: "There is no abort"
BOOM!
One semi hit the car before the other and, as the trucks collided at 35mph, the car got spat got spat out sideways.
Jame: "It wasn't quite right but I don't think we can reset"
The trucks were nowhere near fused together. Instead there was lots of shrapnel everywhere.
Although they hoped the collision would have been more square-on and simultaneous, an important component of the myth -- semis fusing together on impact -- was busted.
mythbusted
Random tidbit: it took the cast and crew (all hands) two days to cleanup after this myth