Swimming is good for muscles, breathing apparatus, heart and blood vessels, development of endurance. In addition, it is very useful to overcome fear of water in order to feel comfortable on lakes, rivers and the sea.
Nowadays videos are in vogue - they are taught to ride on them from the age of 4, less often earlier. Small children do not fall high, but useful for coordination.
Hockey - we have a hockey section near our house, in winter they ride on ice with sticks, in spring and autumn they do exercises and run
Dancing will be useful for girls - the same exercise, only to music
It is important to know what the child likes! And active circles are always great
Everyone chooses preferences for himself, you just have to offer, tell and show, and the child himself will choose what is more suitable for him and what he wants to do. As for me, dancing is suitable for both girls and boys, classes contribute to the correct development of posture, and the child becomes more self-organized. Moreover, it is never too late to go to dance, there are schools where children of different ages are taught sports dancing, for example, as in this Moscow school maximum-dance.ru
I think that sports are preferable in which the child can develop and grow, and not stand still. It often happens that classes burden the child and at a time when peers are breaking records, he does not strive for new successes.