I'd have to come down on the side of 'ethical' (though, obviously, "we want to do some research on a child population that relatively few people care about!" science should probably face additional scrutiny, as a genre); because, from the perspective of the research group's ability to change anything, they are really just observing a natural experiment, not arranging one themselves.
Not really any different from an epidemiologist or toxicologist studying employees of ACME Toxin Smelter in order to determine the effects of some flavor of chemical exposure on human health. It'd be crazy unethical to do direct studies by exposing people to the compound.
It isn't as though they could make the situation more ethical by looking away and ignoring it, nor less ethical by keeping detailed records.