I am eligible to use drop box for stamping, can I apply my son's H4 stamping with my H1 and wife's H4 using dropbox?

My H1-B visa and my wife’s and son’s H4 visa expires in November 2014. The extension for both visas is in process. After going through the US Travel Doc website, I think that I am eligible for using Drop Box. But the website mentions that kids need to have copy of parent’s valid visa to use drop box. My question is, if parents are also applying for stamping, then can the kid apply along with them using drop box OR should parents get their visa stamped first, and then kid needs to apply later (using parent’s new visa copy)?