Yes and no, you will need the the GCC, COC, or test results from the blanks manufacture if the bodysuits (Gerber holds the trademark on the word "onesie" & you can not use it to describe another company's one piece clothing). This is because most bodysuits use metal or plastic snaps to hold the front to the back of the garment, now if the bodysuit uses velcro which is on the exempt material list then you do not need the paperwork. Also keep in mind that since most of these types of bodysuits are for children 3 and under there may be additional testing concerns for the 6 limited phthalates.
There are currently no exemptions from the phthalate testing, though the last I heard though a advocate group for the textile and garment industry was seeking an opinion from the CPSC as to forming an exempt raw material list for phthalates in addition to the lead exemption list.
For the final item to be exempt from the lead testing it needs to be made of 100% exempt raw materials, that includes any embellishments and labels (& the label ink) that are included on the final item. Currently if something is added to the fabric (keep in mind not all types of fabric are exempt) or added to the final the product that is not exempt and you can get either test results, a GCC, or COC that gives the lead and other compounds that need to be tested for in PPM with the labs name and date of testing then you do not need to retest the raw material or the final product. Just remember that may change the things about component testing, exemption lsit, or the stay of testing in the future so sign up for the e-mail updates at the CPSIA.
For the current full list of raw materials offically exempt from LEAD testing please read
http://www.cpsc.gov/businfo/frnotices/fr09/leaddeterminationsfinalrule-draft.pdfAn update on the stay of 3rd party testing
http://www.cpsc.gov/cpscpub/prerel/prhtml10/10083.htmlE-mail updates
https://www.cpsc.gov/about/cpsia/cpsialist.aspx
