My DS7 is very social and still doesn't play well by himself. He even tries to draw us into his video games! He is exhausting to me, an introvert, and the only way to disengage him is to have a friend around. DS1 will play with cars or blocks or watch TV or paint or otherwise occupy himself for refreshing blocks of time. My mom says it's because we spoiled our firstborn, but it seems innate to me. My firstborn is very much like my husband who would rather interact with anyone than be alone.