More information about your trailer will help you get a better answer: make, model, year, etc. Generally when you are plugged into shore power, the converter charger in your trailer will charge the house batteries.
This all depends on:
1) Does your trailer have a converter/charger?
2) Does your trailer have a master Disconnect Switch? And is it in the ON/Connect position?
3) Are the trailer batteries any good?
4) Was there 120v AC in your trailer when you were plugged into shore power? In other words, was the converter/charger receiving 120v?
5) What items/appliances were connected (Turned ON) when you were plugged into shore power?
6) How much battery capacity was there prior to plugging into shore power?
LeRoy