The first three seconds matter. You can’t get them back. Everyone forms first, strong opinions in these fleeting moments.
So, all young children need to learn greeting basics. Practice them constantly with your children.
In my office, when first meeting a child, I know which parents have (and which haven’t) spent time training their kids on the greeting basics. The kids who get these simple steps down early, I’ve observed, go on to be happier, make more friends, handle new social situations more easily, aren’t as self-conscious, and act more confidently.