Hello Erika!
I would HIGHLY recommend going to Magic Kingdom and Hollywood Studios twice during your Disney vacation! I have five children, and these are the two parks my kids ALWAYS want to visit again and again. There is just SO much to do, see, ride, and experience at Magic Kingdom AND Hollywood Studios!!
You will not have to stay from opening to closing to experience everything each park has to offer. However, I would recommend getting to the parks when they open to the general public. The parks are less crowded at this time, and it will give your family a head start in riding all the attractions before the big crowds arrive. (That would be about an hour after each park opens.)
To help you begin planning for your very first trip to Disney World, click
HERE!
If you have other questions, please let me know!
Have a MAGICAL day!