Two years ago I traveled with my five month old, a two year old and a four year old. The best tips I can give you: Bring your own stroller we took a double stroller the 5 month old used the back and the other two would swap when they wanted a rest we took it on the plane with us and checked it at the gate no prob. another idea with the stroller is get an insulated backpack you can put it on the back of the stroller and use it to store drinks since its insulated if you put a ice pack with it you could I suppose put your formula in there too, but I used to make mine as I went to avoid spoilage.
Some kids won't drink water (my daughter does, but my son refuses) so what I do is use a funnel and pour some Koolaid mix in the water bottle (presweetened of course). I didn't make it according to package instructions I made it very watery, but enough taste to satisfy him.
I would bring a mini first aid kit with you and pack some diaper ointment, infant tylenol and gas drops you would rather be with than without. Oh and don't forget the tylenol for yourself
A lot of strollers out there are very dark in colors that makes the babies hotter, so what I did is put the shade over the stroller and bring a white towel and drape it over the shade so the sun reflected off the towel and then you have a towel if you happen to need it comming off a water ride or something. I would also wet the corners and wipe the faces and necks of the kids to cool them off.
Don't forget the disposable ponchos because no kid wants to sit in a wet stroller (I can't blame them) If it looks like its going to rain before getting in a ride or show cover it so you wont have to worry about it when you get out.
Listen to the kids when they are getting cranky take a break,
Don't forget the breaks, We never went back in the parks at night the kids would have gotten to exhausted so we made a plan of what we wanted to see and made sure we added in where to eat for lunch and where the break attractions were- Hall of presidents (its cool and they always fall asleep) Train around MK the breeze is nice and again they fall asleep- if you plan it out and get there when the parks open important- if you want to do some of the big rides using baby swap- and you are not going to be going out of the park for rests, you will have a great time!!!!