Hello Jennifer! Welcome to planDisney - it's always a pleasure to answer questions from a fellow Arizonan.
It sounds like you are well on your way to planning a fantastic day for you and your little ones. My wife and I have two young kiddos as well, and from our experience, it has been ideal to visit
Fantasyland as early in the morning as you can.
When we've visited, the lines for Fantasyland attractions get longer throughout the day and have tended to peak by around dinner then will usually start to shorten (or remain constant) until closing. Though, since you're visiting with two little ones, I'm guessing you won't be sticking around that late. Additionally, though it will likely be nothing compared to our peak summer weather here in the Grand Canyon State at that time - it will get pretty warm in the afternoon.
Having said all of the above, here would be my suggestion for structuring one magical day at Disneyland Park with your little ones.
I'd plan on getting to the park as close to opening time as you can - even better if you can make it into the park for "rope drop" when the park officially opens (you can enter the park and wait on Main Street, U.S.A. - grab snacks for the kids and a coffee for you!). After the park opens, I would head straight to Fantasyland! All of the rides in this land are so much fun for families with little ones, but I would prioritize
Peter Pan's Flight as this one seems to have the longest line. This should definitely cover your first few hours in the park, so just take your time and soak up the magic with your kiddos!
Next, you could head over to New Orleans Square to ride
Pirates of the Caribbean (this does have a small drop near the beginning, which made our oldest a bit nervous on the last trip but he ended up loving the ride). Next, you could try the
Haunted Mansion (though this can be a bit spooky for some little ones) and then head over to Critter Country for
The Many Adventures of Winnie the Pooh.
It should be around lunchtime now, which is a perfect time to head over to
Mickey's Toontown! Grab some picnic items from
Good Boy! Grocers and find a nice green spot to relax and eat. There is a lot of fun in this area, then after that you could head to
Pirate's Lair on Tom Sawyer Island or explore the rest of the park.
I'm clearly running out of room for a response here, but I'm hoping this will help you start your day well. Thanks again for your question, Jennifer, and have a great trip!
Have a Magical Day,
Greg