Hi there, Karla! Thanks for visiting the Disney Parks Moms Panel and asking your question!
Your kids are at such fun ages to take to the Disneyland Resort and your 4-year-old has hit the magical 40" height mark! If your preschooler is up to it, he/she can now ride
attractions like Radiator Springs Racers, Space Mountain, Star Tours - The Adventures Continue, Big Thunder Mountain Railroad, and a few others with shorter height restrictions. Whenever my family is at the parks, we usually have a backpack and I have a small purse that we take with us on every attraction. There are typically small bags in the ride vehicle to slip your belongings into or for most attractions you can simply place your backpack at your feet while you ride.
If you are bringing along items that you won't necessarily need on-hand all day, consider
renting a locker. There are lockers located in each park and right outside Disneyland Park for your convenience. Also, if your youngest is in diapers or starting to potty train, you might want to use the
Baby Care Centers. They offer large changing tables, restrooms, rocking chairs, and sell baby essentials and over-the-counter medication as well.
I hope this helps! Have a magnificent visit to the Happiest Place on Earth!
-Linda