Idea 4: It's Friday - HIS day!
Friday is dedicated to Imam Mahdi (aj), and he will reappear on a Friday also. As with the other days that are linked to the other Ahlul Bayt, there is a small ziyarat for our Imam that can be recited today: http://www.duas.org/WeeklyZiyarat/friday_z.htm
Or if your children are younger, why not just recite Dua Faraj with them to mark it, and pray for his reappearance?
Taking out sadqa for the safety of the Imam is also highly recommended today!