I would stay. Quality of life in the US sucks. I was a manufacturing engineer, and the lifestyle and pay were not worth it. I was an exchange student to Germany after high school and ended up living there for 5 years, ending a decade ago. I’d go back in an instant. Learn German regardless of how long you stay. Once you find a circle of friends you will have the kind of friendships you are looking for. Since you have until now not intended to stay in Germany, the locals probably won’t get too involved with you. If you become more permanent, so will your relationships.
If you have a secure support system that’s a plus. If they bugger off, no more support system where would you be better off? Remember health care, child care, time away from work, maternity/paternity leave in the U.S. are just suggestions. Most people go without these or are run ragged trying to get them. From what I hear Australia/NZ do a better job of making child rearing doable. The U.S. is not considered one of the better countries to have children in.