Between 12 to 18 months baby becomes very mobile. They will have mastered crawling, walking and will begin running. Baby's ability to move purposefully will correlate to the learn to swim lesson. Babies will swim through the water using primitive swimming actions that often resemble a dolphin like wriggle or their land crawling action. These early swimming attempts allow baby to become increasingly independent in the water and capable of performing water safety skills such as turning underwater and even returning to the side of the pool.

Baby's comprehension is also starting to improve. They can follow simple instructions and may group objects by shape, colour and size. This increased comprehension means that if a baby is regularly exposed to water through swimming lessons and water play they will begin to learn their boundaries and gain a respect for the water. Adult supervision at arms length is mandatory during all water based activities.