Use mat as aid

Use a swim mat. Have the child lie in the airplane position on the mat, and correct their leg and arm positioning as needed. The child should then place their face in the water and hold their breath for five seconds. After practicing several times with the mat, you can remove it with prior warning. The mat provides stability, allowing the child to lift their legs off the floor effortlessly. Alternatively, you can support the child with both arms, but this is less convenient.