One tip I would give having gone with little kids many times is bring snacks! Even now that the twins are 7 and I often go without them I still bring snacks because its convenient and cheap. I pack a backpack with half frozen plastic bottles to drink and lots of the handy little things like fruit rollups and rice crispy treats...anything that is individually wrapped and wont melt or make a big mess.
Kids get really impatient but if you give them something to munch on those impatient tempers can be turned off like magic!
Those little pocket sized travel toys can be handy too with the very young when you need to get them to focus away from hussle. I'm thinking like etch a sketch/magna doodle type things.
bugs land is a great place to hang out because it tends to be much less hectic than fantasyland with plenty of shade and lots of kid friendly rides with relatively short wait times. The only thing in that area that young ones might not like is the tough to be a bug show. It can be scary to the little ones.