Why didn’t he and his friends tell their families they were leaving or where they were going?

In A Long Way Gone: Memoirs of a Boy Soldier, Ishmael, his brother Junior, and their friend Talloi travel to Mattru Jong to perform a dancing and rapping act. Their decision to travel without telling anyone, including their families, where they are going results in their being separated from their families once their home village is taken by the Revolutionary United Front (RUF).
The decision to not tell their families where they are going is, unfortunately, quite naive. Keep in mind that these three are quite young at this point in the story. They do not truly consider the negative consequences of leaving without informing their parents about where they are going. They assume they will return to the village the next day before any fuss is made or any significant events take place.
While they should not have left without talking to their parents, especially given their age, their youth should make readers sympathetic to the fact that they could not have predicted such a horrific series of events would take place in their absence.