Stop paying taxes to fund wars and economic sanctions that force people to flee their countries trying to make better lives for themselves.
And stop treating their kids like shit when they do come to your country.
Help them integrate.
Youth violence is a societal problem.
Remove the migrants and the violence stays exactly the same.
Lack of opportunities, poverty, boredom.
From my own experience the ones causing problems have parents who work 14 hours a day and therefore the kids are emotionally neglected.
Kids need love and acceptance from their families and the wider community.