On our first trip my son was so excited he was up at 3am, having arrived at 9pm the night before !!
We've learned a couple of things since then - e.g. keep them up as long as possible on the first night - maybe go out for a meal as they are so excited. On on the first day, we then don't do too much and have an early night, the kids are then fully charged for the rest of the vacation
Have fun
A.