My gf's DD didn't do 3 year old kinder. And she's fine. I think it is a child by child basis. She had an older brother and a younger sister. And when she started 4 year old she already had friends there from outside kinder.

I chose 3 year old because DD was an only child. I didn't like the idea of child care for socialising. I think this is more important than anything. The socialising. My gf is one of those amazeballs mothers who walks to the park everyday, meets people with kids, gets out in the dirt with her kids etc. so her daughter was more well rounded than some of the others.