Moldavians see EU passport and child document, they do not care because airline must pay when passengers are prohibited to enter the country and airline must return them. I am sure that German border would not let you in from Moldova with your child Russian passport and it is not just me and LH who do not see your right. I see yours and your spouse right to move freely to and within EU but not your child as only a Russian citizen per valid document. After valid Brexit your family will face even more difficulty or even entry denial as Romanian/Russian citizens in UK if everything goes as the Government of UK has planned.