Hi Kathy,
Welcome to the Disney Parks Moms Panel! October is my all-time favorite time to visit Walt Disney World and Mickey's Not-So-Scary Halloween Party is the number one reason why! Not only that, but there are so many yummy treats, spook-tacular decorations and fun activities that are only around at that time of year.
Your idea to
rent a locker is a great one! If you're not familiar with the location of these at Magic Kingdom, just head to the right when you enter, but before you go under the train station. There are two sizes available to rent for a daily rate and refundable deposit for each locker key. The small is 11" h x 9" w x 16" deep and the large is 17.5" h x 12" w x 16" deep. There are more of the small size than there are of the large size, and during busier times, the large ones sometimes do sell out. If that happens, you always have the option of renting more than one of the small size, though. Since lockers are rented on a first-come basis, and since the rental fee at Magic Kingdom is a per-day rate, I'd recommend making that your first stop when you get to the park for the best chance at getting your first choice.
I hope that helps, and wishing you a
frightfully good time, Kathy!
Beth