Children need only a single word such as "baby," and a peculiar way of saying it themselves, to laugh aloud in the next 10-15 minutes, or until another source of happiness catches their attention. They simply repeat the word in that unique way of saying it, again and again, milking it with all the joy they can get from it. They have the simplest need to make themselves happy, and are very efficient in enjoying that source of joy. Things that adults have learned to forget to their sad misfortune.