I thought I'd add that I have a number of school classes in different parts of the world that I send postcards to when I travel. My destinations are so diverse that one school's classroom has a 'Father Bill' map on their wall. On the cards I send, I try to give a bit of information about the city and I ask questions (usually more than one) so the children can work in teams to find the answer.
If you know of any business travellers, you may get them to participate in sending cards to your children.
I wish you every success
Fr. Bill