The Germans were concerned that carrier pigeons would be used to communicate with Soviet forces. Carrier pigeons were used extensively during both World Wars.
From the Rostov-on-Don tourism website:
Черевичкин Виктор Иванович (1925–1941) – ростовский пионер-герой.
Когда немцы в 1941 году взяли Ростов-на-Дону, они приказали городским владельцам голубятен уничтожить всех своих птиц. Гитлеровцы опасались, что с помощью почтовых голубей ростовчане будут передавать советским войскам разведывательную информацию.
Но Витя не подчинился приказу и тайно продолжал держать голубей, с их помощью наладив связь с партизанами. Но был «раскрыт» и арестован. Перед тем, как его увели на казнь, Витя успел выпустить всех голубей на волю.
На Нюрнбергском процессе фото убитого мальчика с голубем в руках было представлено в числе документов, обличающих фашизм.
В 1954 году был включен в официальный список пионеров-героев, выпущенного в составе Книги почета Всесоюзной пионерской организации им. В.И. Ленина.
(English translation from the site)
Cherevichkin Viktor Ivanovich (1925-1941) - Rostov pioneer-hero. When the Germans in 1941, took Rostov-on-Don, they ordered the town pigeon owners to destroy all their birds. The Germans feared that using carrier pigeons Rostov will send intelligence information to the Soviet troops. But Victor did not obey the order and secretly continued to keep pigeons, with their help he established the connection with the guerrillas. But he was "discovered" and arrested. Before he was led away to death, Victor managed to release all the pigeons loose. At the Nuremberg trial a photo of a murdered boy with a dove in his hands was represented among all the documents denouncing fascism. In 1954 he was included in the official list of the pioneer heroes, released as part of the Book of Honor All-Union Pioneer Organization of V.I. Lenin.
The Vladimir Lenin All-Union Pioneer Organisation was a Soviet youth organisation not dissimilar to the Scouts. As the Wikipedia article observes:
During the Second World War the Pioneers worked hard to contribute to the war effort at all costs. Thousands of them died in battles as military personnel and in the resistance against Nazi Germany in its occupied territories as partisans and Pioneers under secrecy in enemy-occupied towns and cities, even in concentration camps.
So it is entirely possible that the boy in the picture was a member of the Pioneers, and that he had been actively using his pigeons to communicate with Soviet forces. (It is equally possible that he had been shot for simply having pigeons and thus being suspected of communicating with Soviet forces.)
It is worth noting that the case of Vitya Cherevichny was mentioned in the records of the Trial of the major war criminals before the International Military Tribunal, Nuremberg, 14 November 1945-1 October 1946, Volume 7, p455. The record states simply that:
"In Rostov-on-Don a pupil of the commercial school, 15-year old Vitya Cherevichny, was playing in the yard with his pigeons. Some passing German soldiers began to steal the birds. The boy protested. The Germans took him away and shot him, at the corner of 27th Line and 2d Maisky Street for refusing to surrender his pigeons. With the heels of their boots the Hitlerites trampled his face out of all recognition."
Note that this makes no mention of Vitya being a member of the Pioneers or of any suspicion that he was in communication with Soviet forces.
I haven't (yet) found an English translation of the "official list of the pioneer heroes", released as part of the Book of Honor of the Vladimir Lenin All-Union Pioneer Organisation, but I suspect that you'll find more detail there.