Did your kids meet any kids in the host country? Did they exchange addresses/e-mail addresses?
Pen pals (e-pals?) are a great way to keep the travel spirit alive. Visiting a pen pal on a later trip is a great thing. Maybe she could visit your child's school when she and her folks visit the U.S. next fall? If you did exchange any addresses and need to get the correspondence started, sending them a photo you took of the two kids together is a good way to start.
When I was in high school, I actually went to an “International Youth Conference” in Israel. I met a number of people there and kept in touch with a few. I've visited one friend from London 3 times now (even more, both of our parents are now friends and visit each other).
Speaking of photos, we stumbled on to something one trip when we forgot to drop the film off to be developed. A couple of weeks later we realized that a roll was still in the camera, and so we got it made into photos at that late date. It was great!
Seeing the photos weeks later, when some memories had already started to fade was an invigorating event. It woke up all sorts of details we thought we had forgotten. Instead, we found that the details were just in a dusty cabinet in our heads, waiting, waiting, waiting for us to one day pull them down to enjoy the pleasure of their company again.
Now, this might be different in the digital age. These days, I would strongly encourage you to tag and label your photos when you get home so you don't forget all those details that fade with time.