Children live in present

Am following a blog "etc." on parenting. In the recent post the author has described how a 4yr old child meets a stranger child in a park and then play together on their own. The post talked of adults inculcating this quality of children of becoming friendly with people in first meeting.

Was thinking as to why adults find it difficult, which children do so easily?

Some reasons, which came to my mind are-
-We as adults keep losing our selflessness ,which was readily available with us in childhood
-Adults live in past mostly having regrets for things not done or worry about uncertainties of future. Children live in the present moment and so are always happier, friendly and cheerful.
- Adults generally remember,what they should forget and forget, what they should remember.Thus building new relationships and maintaining existing relationships is not easy for them. Children are outgoing and value love so find it easy to build new relationships .They also forget and forgive easily and thus are able to maintain existing relationships.

Each one of us has a child in our hearts and we have to be in touch with him to be childlike.