I was just about to write about my 20 months old dd! Like your son, she has stopped napping about 1 week ago and I am at a loss for what to do. The only time she will fall asleep is when I am running errands and she naps in the stroller. With the extreme cold we are currently facing I have not gone out.
The only thing I can think of is that they might both be teething now.
I am hoping this is not the end of her nap because I probably need it more than her
Hope someone out there has suggestions.