Welcome to planDisney, Irina!
You can absolutely leave the park and re-enter on the same day! This will provide lots of flexibility to how you plan your day at the Disneyland Resort. For instance, you may want to enjoy dinner at one of the amazing restaurants in the
Downtown Disney District, but then go back into Disneyland Park later that night for fireworks. Or, if you are staying at a Disneyland Resort Hotel or a nearby Good Neighbor Hotel, it's easy to head to your room for an afternoon break or nap. Additionally, if you will be
parking in a Disneyland Resort parking lot or structure, you may leave and re-enter without paying twice. Simply keep your receipt to show to the parking attendant when you return.
To add even more flexibility to your park-touring plan, consider
purchasing Park Hopper tickets. With a Park Hopper ticket, you can hop between the parks starting at 1:00 p.m. each day. Disneyland Park and Disney California Adventure Park are so close together that park hopping takes mere seconds. My family and I park hop every day of every trip we take.
I hope this information was helpful. Have a great time at the Happiest Place on Earth!
-Linda