Learning to kick properly in swimming is much more complicated and unnatural than we first think. Babies come out of the womb with a protective reflex, and when placed in water resembles a ‘frog’ type kick, hence why many European countries teach breaststroke first. Following this, one of the first major motor skills children learn to do is to walk/run. Children often want to go fast in swimming and they associate going fast with ‘running’. Running involves bending the knee. They are also learning to ride a bike about this age. Bending our knees in swimming is only going to cause the swimmer to push and pull the water around in circles. We want the kick to start from their hips, limited bend at the knees, and a ‘flip flop’ movement in the ankles to push the water back behind them and consequently propel our body forward.
Even though we work on ‘straight legs’ from about the age of 3, most swimmers don’t perform his motor skill correctly until much later, especially for boys. It’s not common for boys to want to point their toes, they especially want to go fast or ‘ride their bike’. Even though we don’t like to put an age on acquisition of skills, boys have quite a development in growth and coordination about age 7 and so you might see the straight legs come in to fruition about then.
Even from the age of a baby, it is helpful if parents use key words to build up their word association with the movement you want. A 6 month old won’t kick on command, but doing ‘cuddle kicks’ while saying ‘kick’ will significantly help their development in so many ways. After a while though, some toddlers will stop kicking on demand. Sometimes it’s because of their will for independence (I won’t kick when you tell me to, only when I want), or because there is so much going on for them where they are discovering their legs, feet, and what they can do. It does not mean they are going ‘backwards’, quite the contrary, this is the time that neural connections are occurring all over the brain and they will come back stronger with time. It’s a good time to repeat but to offer variation and keep it light and fun.
There are some things (apart from bringing them to lessons) that we can do when they are 4+ to help this movement that really only occurs in swimming. Here is a video below that shows children can sit on the couch or their bed and do this movement. From experience we find swimmers who do this for 20 seconds every day for a week make a big improvement in coordination and strength. https://vimeo.com/manage/videos/847170478