I used Nan HA with DS from the time he was 2 days old. I switched over to S26 Gold when he was about 2 weeks old because he got really bad constipation from the Nan. (Which is unusual because S26 usually causes it) but he has been fine. I only put him on the gold one because that was the one my sister used, and she gave me some free samples when I was in the hospital, so it was all I had at the time!!!