Veratrice, since the dress is reversible, you may put all the required FTC and CPSIA information on a hang tag attached to the dress. This is one of the exceptions to the permant labeling. If the item is too small or if the label would interfere with the use or asthetics of the item then you can hand tag it.
And no, for all of you that just don't want to tag, it has to be real, not just because you don't like how the tag looks.
Buttons do not have to be labeled a chocking hazard, as their very purpose needs them to be small. BUT, you better be sure to sew them on well, because anything that comes off easily can be called a chocking hazard.
So a couple of loops threw the holes and a whip stitch on the back would not hold it on.