You should communicate with him about your work scedule when you rolled on his team and never late to share this with him the next week, explain the reason that you need leave at 5:30pm to pick up your kid when you have chance, a reasonable manager will understand it and will have no nagitive feeling about this. I have this situation all the time, I always shared what I need with my manager. Call him is not necessary at this time since it is his private time now , not work time, but find a chance to talk to him next Monday. You may raise a topic about kids if he has family and child, so it is easy for you to drive to the topic you want to discuss.
Good luck,
