To me (and Im not an expert by any stretch) it should include a full body warm up as well as shoulder specific stuff and of course throwing.
A good dynamic warm up lasting about 10 minutes. Full body movements.
A few sprints. Arm circles, a band routine (my son uses the Jaeger band routine), abridged longtoss, then to the pen.
It can vary person to person but when I see coaches giving kids 10 minutes of time to do static stretches then throw a few in the bullpen before coming in it drives me nuts.