I can't help signing. Mainland residents, no matter how old they are or whether they are adults, need to show their travel passes to and from Hong Kong and Macao and valid endorsements. Babies need to be accompanied by their parents to the immigration control department. The required materials are the baby's household registration book, the parents' ID card, and the supporting documents reflecting the guardianship relationship (if the parents and the baby are in the same household registration book, the household registration book is enough or the medical birth certificate). So children under 2 years old can't go to Macau without a visa.