Yes, coupling failure's in there. (Tried to C&P but phone wouldn't let me).
The way i look at it is if a google search brings up nothing it cannot be a big issue so its down to the parents whether they think the very small risk is worth taking, i would still rather use a tagalong than have a young child in front of me on their own small wheeled cycle i think there is a far bigger risk of an accident when you have no control over them on their own cycles at the age you would use a tagalong.
I did google "Tagalong coupling failure" and come up with nothing.
(apart from one product recall from several years ago)