Question

Why do you think Hitler had German children join Nazi organizations?

Answer 1

To strengthen his grip on society and create an ideologically pure base for his dictatorship.

Explanation:

Here you need to think at how a dictatorship works; the dictator needs to control every aspect of social, economic and political life to maintain his power but this is complicated. A dictatorship starts and has to deal with young people, adults and old people with their already formed ideas, beliefs and political orientations. This is difficult and normally to cope with dissidents the dictator uses violence and segregation (Lagers, Gulags, Killing Fields, etc.).

But, what if you can "shape" the new generations to change them into faithful followers?

You can start from the kindergarten as an innocent game with uniforms, wooden rifles, parades, "military" training and drills to introduce in the minds of the children the idea that the state is caring for them and so they must "protect/take care" of the state. The state becomes the new family that must be protected, respected and cared for against all the bad subjects that (wrongly, of course) are attacking it.

These children will become the base for the future of the dictatorship. They will accept every command from the representatives of the state even the most absurd or inhuman without remorse or complain.
Sometimes they will be even used to spy on the "treacherous adults", like family friends or even parents, reporting their defeatist comments to the Gestapo.

In Nazi Germany the male children were enrolled in the Hitlerjugend organization while girls were enrolled in the Bund Deutsche Mädel organization.

As an organization in Nazi Germany, the Hitlerjugend was incredibly powerful leading to the formation of one of the most feared Panzer-Division of the Waffen-SS. The Hitlerjugend Division fought against the Anglo-American in Normandy and was feared and hated for their fanaticism and cruelty in combat (the Canadians, in particular, loathed them).