We started this probiotic with our baby when she was 4 weeks old, as she was born by cesarean, while I was on antibiotics. She is exclusively breastfed, and I wanted her gut to be able to access all the good of BM. She was also incredibly gassy and seemingly uncomfortable at night. Within several days of starting this, her gas basically disappeared, and she seemed much more comfortable at night. I won't say she suddenly slept like a peaceful angel, because she's a baby after all, but she did sleep better! It took her a little bit to adapt to take it from a syringe so young but she got it after a while, and now at 6 mos, she sucks it down no problem most days.