Is "Jungs" a relatively new (post WW2) word in German? I have heard German spoken from my my parents on occasion since a child, from my relatives when I have visited Germany and traveled in Switzerland and Austria but have never heard the word "Jungen".
"Jungs" is a bit informal and used pretty commonly, not only for children but also for sports teams etc. "Buben" is a bit outdated, but still in use by elderly people in south germany. "Jungen" is used pretty seldom for boys younger than about 10 years. In official publications your most probably will find a formulation like "Jugendliche" or "männliche Jugendliche" (for boys >10 years).