The 'Islamic State of Iraq and Syria' (ISIS) claimed responsibility for the attack, which comes before the start of a unilateral cease-fire declared by the Afghan government with the Taliban.
The explosion took place about an hour after the Ulema Council issued a fatwa declaring suicide attacks to be haram and urging the Taliban to join the peace process.
Teenagers recruited by ISIS, whether voluntarily or by force, are being given a second chance at a centre where they participate in sports and learn history, geography and 'morality'.
The three brothers were on track for a bright future until their lives were cut short. Before they could exact revenge on ISIS for killing their father a year earlier, the terrorists struck first, leaving the brothers' family in ruin.
The Taliban's declaration of war will not undermine the Afghan government's resolve for peace, officials say.
The Independent Election Commission, which is overseeing preparations for the vote, hopes to register up to 14 million adults at more than 7,000 polling centres. Militants have repeatedly tried to disrupt the process.
Recent attacks on Afghan journalists and on the voter registration process are 'far from every religious, judicial and international law or regulation'.
The second of the two suicide bombings was timed to hit first responders and journalists who rushed to the scene of the attack, officials and witnesses say.
An ISIS suicide bomber killed more than 60 and wounded more than 120 civilians, including children, at a voter registration centre in Kabul.
Ravaged by air strikes and declining morale, ISIS in Afghanistan has responded to its increasingly desperate situation by manipulating society's most vulnerable members -- children.