What happens if I have overstayed my 90 days in schengen territory without having an entry stamp when I arrived? Can they see that I have been here longer then my stay? I have stayed to marry an eu citizen ,French, who we have been together for 6 years and have a 3 year old who is a dual citizen of france. We plan a marriage in oct. but I have been worried about the fact I have overstayed my 90 days here and I no proof of when I came here? Do you think when I return to states to get a marriage visa there could be a problem? Or can I obtain a visa here?

You may have to explain why you overstayed and failed to have your passport stamped, etc. when it comes to change of status. The authorities have all records so this issue will surface immediately.

You should consult an experienced immigration attorney.