in other countries, expressions doesn't translate well in English. I think the thing under mum's apron resembles that you can't do anything on your own without your mum's help or approval. ( still a child depending on his mum.)
In other words why do you have to sow off your WW2 knowledge and get offended by that?
To use Dunkirk as your battle thought, shows you don't have a clue .
Germany was fighting on the east and west. Also the ally troops were fighting for a good reason .
So it you use something like that remember this .less we forget .