SAME THING HAPPENED TO ME AND MY KIDS - Different outcome.
Flight SFO to FRA on United. Wife and two kids. At SFO we presented our passports to 3 or 4 different people in UA. Boarded plane, arrived in FRA. I might have the order wrong but it seems to me you pass we had to present our passports to two more officials (customs) before we reached boarder control and were allowed in enter Germany. At that time we told "There is a problem". We were told the kinder's passports would expire while we were in Germany. (We didn't know kid's passports were only good for 5 years.) We were allowed entry and told we would not have any problem traveling in Germany with expired passports. But we would have to go to the American consulate to obtain a temporary passport in order for my children to leave the country.