Oblivious Dad, Disappointed Big Brother
Being the older sibling is fun, but it also comes with a ton of responsibilities. This boy right here is starting to learn just that. While his dad was still oblivious of the mess his new sibling made, he already knew he was bound to clean up after him or her one way or another in the future.
If their mom and dad do things right, the two of them will get along quickly. Many parenting books and blogs emphasize the importance of properly introducing an only child to a newborn sibling. Their natural reaction would be to be jealous or confused. The big brother instincts would kick in later.