Until recently, our house has been full of two babies. Or a baby and a toddler. Or two toddlers. Or a preschooler and a toddler. At all of those stages the children have been very parent focused. At first it was just crying, and then came the "Mommy, Daddy, come play with me stage." It was as if they had no toys or space to play in unless an adult was at their side. They simply didn't seem to know how to play on their own. (Notable exception: Michael can play for over an hour in his room if he is supposed to be falling asleep.)
Recently I am beginning to see glimpses of a more independent future. Michael in particular will occasionally become absorbed in a self-directed activity for 30-45 minutes at a time. When an older playmate comes over, they will all disappear for half an hour at a time. They are beginning to see each other as playmates instead of always depending on me. Michael will "whisper" something to Ava that he doesn't want me to hear. (His whisper needs some work, I can pretty much always hear what he is saying.) They will converse with each other in the car. As long as they are not the one causing the other to cry, they will try to comfort each other when someone is upset. When Ava is away (at her grandparents, taking a nap, off to a therapy session, etc.) and returns home, the first person she looks for is Michael.
It is wonderful watching their independence and relationship as siblings develop simultaneously and in an interconnected way. This is what I was hoping for when I made the completely impractical decision to get pregnant when my first child was only 6 months old.