I have just been talking about this with friends over lunch in Sunday!
None of my kids do any extra curricular activities.. At all. Dd2 and DS go to daycare for 2 half days per week and dd1 is in prep at school.
I'm not really in any hurry for them to start to be honest. When I was young I started netball in under 10's so was about 8-9? And DH played cricket and footy in under 10's, so about the same age.
I personally don't really see the need for it when they are so young. Their interests change weekly so I'd prefer to wait til they're a bit older and can choose what they'd like to do as opposed to me choosing the things I think they should.
I never realized how many people had their children doing so much at such early ages. No judgement for anyone, it's just not something we do so I'm interested to see all the different types of activities that are out there.