Just consulted with my (sorry, folks) Webster's New Collegiate Dictionary.
illegitimate, adj., 1: not recognized as lawful offspring: specif. born of parents not married to each other (emphasis added)
Even an dictionary of American English clearly shows that a child born out of wedlock is illegitimate. Blackburn Raver, you are free to disagree, but a few of us have provided authoritative documentation to support our position. Suggest that you may wish to do the same.
I'll happily forego the use of "bastard," as it carries a lot of additional pejorative connotations.