A creole may be thought of as a generation along from a pidgin. The clearest examples are when slaves from many language backgrounds are obliged to communicate with a lexicon from the colonial language but no help with syntax. Their children then create a new syntax with the loanwords. Here is an example from the Jamaican creole.
The Danish population of Eastern England were dominant in the 11th century, as seen in this map.
In the East Midlands there seems to have been a sudden change two generations after the Norman conquest. The Anglo Saxon Chronicle was still being updated, but its English started to look much more like Modern English.