The two best pieces of advice I received before my first trip with kids:
1) Respect your kids' limits. It doesn't matter how much you paid for the tickets, the money will be wasted if you don't enjoy your trip. It doesn't matter how many things you didn't get to do -- what matters is that you really enjoyed the things you did do. It's easy to have a fantastic time at WDW, as long as you do what works for *you*.
2) Remember to feed your small kids constantly, with more frequent snacks than you do at home. There is tons of walking, and excitement, and heat, and schedule disruption. They will need extra food to keep going.
1) Respect your kids' limits. It doesn't matter how much you paid for the tickets, the money will be wasted if you don't enjoy your trip. It doesn't matter how many things you didn't get to do -- what matters is that you really enjoyed the things you did do. It's easy to have a fantastic time at WDW, as long as you do what works for *you*.
2) Remember to feed your small kids constantly, with more frequent snacks than you do at home. There is tons of walking, and excitement, and heat, and schedule disruption. They will need extra food to keep going.