The rule of thumb around our house is when we come back from grandparents or any trip where the night time routine is messed up, it takes 1-2 weeks to get back to "normal". The only way I've found to make it happen and not drag out is to immediately go back to the normal routine from before the trip and stick with it (as much as possible). Usually, my kids will just bounce back into it within a few days. On occasion, I've had to just really wear them out during the day (shortened nap, longer outside play time, more activities that make them tired, keep them up 30 minutes later) so when they fall asleep that night, they are out for the night and that gets us back to the normal sleep habit. I know that may sound weird but it works!