What kind of milk powder is suitable for babies? ——Comparing the third-stage milk powder and the fourth-stage milk powder 1. Formula difference The main difference between the third-stage milk powder and the fourth-stage milk powder is the difference in formula. Stage three milk powder is mainly suitable for babies aged 6-12 months, while stage four milk powder is suitable for babies over 12 months old. In terms of formula, the fourth-stage milk powder usually adds some acidified lactobacilli and probiotics, which are beneficial to the baby\’s intestinal health.