Question: how long will a baby be in size 1 diapers?
Answer: Tip #3: Diapers for girls and boys Average-size baby boys usually move into Size 1 diapers around four weeks old and Size 2 diapers at about three to four months. Average-size baby girls reach the same milestones later, transitioning into Size 1 diapers around six weeks and Size 2 diapers between four or five months.