1. What should myself and my child wear to our session?
2. Can I purchase just the full resolution digitals?
3. Why are digitals more expensive than regular photographs?
The answer is simple. With a print, you can show your family and friends, display it on your wall, it's a memory captured in time that you can keep forever. With a print it is yours but you can't make multiple copies, or put it on a shirt, or make a calendar with it, you purchased a print that was priced accordingly. There are many ways to still make multiple copies of your prints, put them on a shirt, or make them into really nice gifts but the photographer owns the copyright to that file, and it is illegal to do so.
With a digital file, you can print it in any size you like and with any vendor you like. You can print it on a T-shirt or make it into a calendar. You can have Uncle Joe who just bought Photoshop add really cool effects to it and put it on a hat so he can show off to his friends. You can share it all over the internet, and make unlimited amounts of gifts. You can do whatever you want with it. You will also most likely never purchase anything else with that digital copy from the photographer who you paid to take it for you. To make that legal you need a copyright release, that says that the photographer is signing over all rights to that photograph to allow you to do with it as you want and make purchases elsewhere for the same items that the photographer sells themselves and stands behind.