It depends how old is your baby, two years and younger are free of charge. However, traveling with a baby is not recommended. The sea can get quite choppy, and it might get uncomfortable for a baby. In case you want to travel to Gili, pick the largest boat possible – from EkaJaya or Patagonia Express. And also it's convenient to go from Padang Bai, rather than a port on the south of Bali because boat ride is shorter. An alternative is to fly to Lombok and then a super short boat ride to Gilis.