This is a tough issue. I do think that at some point, it is important to teach children some basic manners and cultural expectations for appropriate behavior in certain situations. The reason is not to curb their joy in life, but, rather, to give them confidence when the time comes to interact socially and professionally, so that they will know that they know what to do. For example, my parents took some effort to teach me in very concrete ways how to mingle at parties, shake hands, etc. They modeled it, of course, but they also explained tricky situations, like what to do when you shake hands with someone who does not know how to shake hands, what to do when you have a bore or a shy person at a party, that sort of thing.
At your older kids' age, they may start being able to perceive that others may shrink away from them, but not know why. Kids can pick up on nonverbal cues. So I would want to teach them how to approach things in a confident way, knowing what to do when others are rude, knowing how to make friends and so forth. Does that make sense? It can be taught in a kind, nurturing way, so that your kids see you as their adviser in such matters.
One thing I like about my stepmother, for example, is that she taught her son that when he went to dances with girls, that the girls might act shy and hang about against the wall, but that the girls really wanted to be asked to dance. She taught him how to do it, how to handle rejection, etc., etc., in a very concrete way. I wish someone had done that for me!
So I would not do much for two year old Maria, but Ryan might be ready for some super basic guidance. In a few years, as the complexity of the situations he faces increases, he will know that you are a great resource at how to make friends and so forth.