Well, we can think about why, and try to to minimize risk.

If it's unused, and they didn't control for diet, then it could be that they're eating processed foods. I would be extremely interested in seeing the diet of a family that didn't use a range/oven, and the relative amount of phthalates and the like.

Assuming they are getting good quality food, then an old stove will always have a pilot light on, even if it's unused. I think it would be hard to ventilate the emissions from a pilot light, since most ducted vents have flaps that only open when a fan is on. But...

If it's a modern stove, then an unused gas stove is the same as not having a gas stove at all, since there's no pilot light, unless you have a gas leak.

In my case, I have a modern stove, and no gas leak (it was tested), so I think my situation is probably different than whatever study you have in mind, assuming everything is properly ventilated while it's on.