The Islamic State (IS) militant group is notorious for recruiting, training, and exploiting children and teenagers on the battlefield.
But the same practice is also widespread among other militant "jihadi" groups in Syria, including some foreign fighter factions, who have recruited local Syrian "ansar" teenagers.
And the sons of at least two Russian-speaking militant leaders have been encouraged to take up arms and take part in the fighting.
For 16-year-old Umar, an ethnic Uzbek boy, following in his father's footsteps cost him his life. The young teenager died fighting Syrian government forces alongside his father -- Salahuddin, the leader of the Uzbek Islamist faction Katibat Imam Bukhari -- in Syria's Aleppo Province in late August.
A video released by Katibat Imam Bukhari on August 31 shows Salahuddin paying his last respects to his dead son. The Uzbek militant is filmed bending over the boy's corpse, hailing his son as a "martyr," a "jihadi" who died in battle.
Chillingly, the Uzbek militant says his son's death is just one of many "martyrdoms."
"There are so many martyrs from all over the world here, so our own martyrs are only a very small part," Salahuddin says. "We will not complain about it, we will just thank Allah."
While the video does not specify Umar's age, the boy was reported by Chechen militants in Syria to have been 16 years old.
Uzbek militant commander Salahuddin buries his 16-year-old son.
Umar was likely killed in a failed attempt by Islamist groups including Jabhat al-Nusra and the Syrian group Ahrar al-Sham to overrun the government-held town of Bashkuy in the northern part of Aleppo Province in late August.
Before the footage of Umar's funeral, the video shows sequences of Katibat Imam Bukhari militants fighting in the offensive at Bashkuy.
Reports on August 26, several days before the video was uploaded onto YouTube, said that the rebel attack on Bashkuy had not been successful.
And the video by Katibat Imam Bukhari does not mention a victory, as it would have done had the militants succeeded in overrunning Bashkuy.
Like Father, Like Son?
Salahuddin is a shadowy figure. Although he has appeared -- and spoken -- in a handful of videos, he has made sure his identity remains a mystery by having his face blurred out.
The Uzbek militant leader has, however, ensured that his reputation as a veteran "jihadi" with extensive contacts among the Taliban in Afghanistan is no secret. He is believed to have spent a long time in Afghanistan before coming to Syria, where he met with several leading Taliban figures, including Sirajuddin Haqqani, a Pashtun warlord believed to provide shelter to Al-Qaeda operatives in Afghanistan.
He and his group pledged allegiance to the Taliban last year. The faction regularly fights alongside Al-Qaeda's Syrian affiliate, Jabhat al-Nusra.
The 12-year-old son of Chechen militant Seyfullakh al-Shishani (right) has reportedly joined IS.
By leading his son into battle, and making him a "martyr," Salahuddin is likely trying to enhance his reputation as a "jihadi" leader by showing that his offspring is also filled with zeal for the cause, so much so that he was willing to die for his beliefs.
Children and teens who want to die waging jihad are especially praised by Islamist groups in Syria, including Russian-speaking factions.
Two sons of another notorious militant, Seyfullakh al-Shishani (Ruslan Machaliashvili), who was killed in a failed raid on Aleppo's Central Prison last year, have been photographed dressed in military fatigues in Syria. The youngest child, a toddler named Yusuf, was pictured alongside a group of militants from Syria's Al-Qaeda affiliate Jabhat al-Nusra, while the second boy, now aged around 12, has reportedly joined the IS group.