Florida kings (especially neonates) dehydrate real easily so:
1) make sure the snake is placed into the water to drink. A water bowl in tha cage is not always used by baby florida kings.
2) try a brained pinky:
Brained pinkys are a pinky with a slit cut on the head with some brain matter squeezed out. This can be first done with a frozen pink or try a live pink with the brian matter wiped on from a dead frozen pink.
3) If a brained pinky doesn't work the you will need a small snake.
In nature young Florida kings eat a small snake for their first meal so a lot of captive born babies refuse mice and want snake. Water snakes are good for scenting and so are many of the ground type snake found in their area. I have tried lizards and scentied with lizards but it only works about 10% of the time with the floridana group. They love their snakes for food 
A fresh killed or frozen thawed garter or water snake kept in the freezer can be used several times to "scent" your pinky mouse. Just cut it open and dip the pinky into the snake.
I am sure their will be other ways people suggest getting their florida king started but the snake scent is the one of the ways that always works with the floridana .