Was it common in the Great Depression for women to leave their babies in public places?
No, not common, but it did happen occasionally. In fact, it still happens, but very rarely.
The Michigan state laws are similar to most, and they're honestly common sense. Keep the paintball in a bag if in public. Do not shoot in public places. Let the officers know that you do have it and why your purpose is. Fire it within reasonable hours of the day. Do not simply carry it around in public places (so don't take it to the mall).