The mother thinks that she could've saved him if she had protested and stopped him from joining the Nazi party.
Explanation:
In the poem "Song of a German Mother" by Bertolt Brecht, we can understand that the mother of the death soldier regrets that she did not do anything to stop her son when he first joined the Nazi party.
The mother is mourning over his son's death because she thinks that she could have saved him if she had protested and stopped him from joining the Nazi party.
The mother laments that if she had known what she knows now, her son would have been alive today.
