Complex sentence: The notes are the same for everyone, and with all the children realizing all the adults are gone, they now have the freedom to do anything they choose and celebrate: but Jimmy is sad that his parents didn't even say goodbye before they left.
Split into simpler sentences: The notes are the same for everyone, and with all the children realizing all the adults are gone, they now have the freedom to do anything they choose and celebrate. However, Jimmy is sad that his parents didn't even say goodbye before they left.