Hi there Rachel,
Welcome to the Disney Parks Moms Panel. The Disneyland Resort is where magic happens every day; I'm so excited for your upcoming vacation!
You are correct, Disneyland Park will be closing early on September 18 for a Special Event. However, the fun for your family does not have to end there, you can still enjoy the magic of Disney over at Disney California Adventure Park once Disneyland Park closes that evening if you have a Park Hopper Ticket.
Sometimes we choose to take a magical break during our vacation to utilize our hotel's pool, if this is something your family may enjoy, you may want to pack your swimsuits and plan to do this that evening. Another option is to stroll
Downtown Disney District, there's always so much entertainment, shops, and dining to experience there!
I hope this helps and that you have a pixie-dusted time during your week visit to the Disneyland Resort. If you have any more questions, please visit me here and let me know how I can help you plan your magical vacation.
Hope you have a Mater's Junkyard Jamboree time at the Disneyland Resort!
~ Lynette