Skin to skin. Scabies is a parasite that causes a very itchy skin rash. You contract scabies by touching someone who has it, or by sharing clothing or bedding with someone who has scabies.
Contact spread. Scabies is a small mite that spreads by direct contact. More than likely, somebody who is infected was holding them or touching them, or the baby was crawling around in a house where somebody is infected. The infection can obviously happen anywhere, but babies often have it start on hands and feet, areas that touch the floor or people. Sometimes it can also come from the dog.
From another person. Babies can get scabies (caused by a mite that burrows under one's skin) through close contact with an infected person.