Congratulations on your first trip! I know very few people who only go once, so I welcome you to our favorite addiction
Since you have children, I would recommend a few tips. Don't think you will see everything on your first trip. Have a few things that each person wants to see and focus on that.
Get to the park 30 minutes before opening, take an afternoon break back at the hotel if necessary, and go back in the evening. (I take my break from 1-4)
When are you going?
Have a basic plan each day. Look at a map ahead of time and have a general idea of which attractions you would like to see and which ones aren't feasible due to interest or height restrictions.
Take lots of pictures. Your first trip is a memorable thing.
Keep well hydrated. Try walking around your block at night as a family. You want to be able to walk a mile without getting winded.
Let us know if you have any specific questions!