OP, you have gotten some really great advice! I'm glad you've decided to go with a stroller. We clock from 12-15 miles or more a day at DL. A stroller will be really helpful!
I agree with all that has been said! Extra clothes in the parks are a lifesaver. As are extra diapers! The baby care centers are amazing! And if your 3 year old is potty trained they have mini training toilets you can use. There are only 2, but they are great and DO NOT have auto flush. Plus, the changing tables are so nice in the baby care centers compared to the ones in the bathrooms.
I'm guessing the 1 year old will be using a bottle still? I would always bring a bottle brush and a small travel size bottle filled with dish soap so I could clean the bottles in the hotel sink.
I would also bring a blanket for in the stroller too. We always use one when my youngest DS falls asleep. Sunscreen and hats are a must! Hand sanitizer and wipes are something I always have on hand as well. I always grab a bunch of napkins wherever we are eating because someone always spills something either on themselves or the table we are eating at, etc. I bring my oldest DS allergy meds, plus Ibuprofen for the kids and DH and I because never fails, we always will need it! Plus I pack a small first aid kit with band aids and neosporin spray.
And as others have said, snacks, snacks, snacks! My boys tend to get overwhelmed by the parks. They are overstimulated. So we take a break every couple of hours and MAKE them have a snack and drink WATER!! It helps them from melting down and gives us all a nice break. When they were little we would go to the baby care center, then take a break on the benches and eat our snacks. We take a whole backpack dedicated to snacks! LOL. We also bring a soft sided cooler with waters, gogurt, grapes, applesauce, etc. We try not to stray from our normal routine/diets while in the parks. We limit to one treat a day and let the kids choose. DS6 always picks ice cream while DS4 always wants a lolly pop. I also bring a bunch of sandwich bags to make individual servings of the snacks too.
Another tip I like to share, probably more for your 3 year old, is that some of the attractions exit you out into a store. For my boys, they had a hard time at first because they would want ALL the toys they saw. LOL. So we had to make a rule that they could look, but needed to wait to buy something until closer to the end of our trip. We would give them a budget and only allow one purchase. It helped SO much and some trips we don't even buy anything now! So you may want to start preparing your 3 year old now so it's not a big deal when you are there. I sure wish someone would have told us that ahead of time!
Last tip, take TONS of photos!!!!!!! My kids cannot get enough! They love looking back when they were little and so do I! Make sure whoever is the photographer gets in some photos too

Have an amazing trip!!!