This suggests to me that the child wasn't wearing one suited to her age. It was too big!
All my kids have worn them. Ds2 wore his from a month old. Both boys wore them until they were 3yrs 24/7 and ds3 has also had his on since a month old. Not once have they come undone on any of the boys and nor do they hang long enough for them to put them in their mouths and the boys never fiddled or play with them either. I have always only bought the genuine good quality ones though.