You can consider gently submerging a baby under water once they are around 6 months old, as they have better head and neck control by this age. However, it’s essential to proceed with caution, ensure your baby is comfortable, and never force a submersion. Always closely monitor your baby’s reactions, and if they show signs of distress or discomfort, stop immediately and give them a break. Before submerging a baby, it’s a good idea to practice blowing bubbles or splashing water on their face to help them get used to the sensation and learn breath control.