Amnesty International - The use of the death penalty for crimes committed by people younger than 18 is prohibited under international human rights law, yet some countries still execute child offenders. Such executions are few compared to the total number of executions in the world. Their significance goes beyond their number and calls into question the commitment of the executing states to respect international law. Since 1990 Amnesty International has documented 90 executions of child offenders in 9 countries: China, the Democratic Republic of Congo, Iran, Nigeria, Pakistan, Saudi Arabia, Sudan, the USA and Yemen. Several of these countries have changed their laws to exclude the practice. Executions of child offenders represent a tiny fraction of the total of executions worldwide recorded by Amnesty International each year. The USA and Iran have each executed more child offenders than the other eight countries combined and Iran has now exceeded the USA's total since 1990 of 19 child executions.
Source: http://www.insideofiran.org/en/human-rights/9290-executions-of-juveniles-since-1990.html
