We will be there at the same time you are (leaving in 13 days) and I finally started getting down to real packing yesterday.
I only have 1 child, but with in park items, snacks, metal water bottles, things to keep him entertained in the room, electronics, etc..... I really started stressing as well. We're up to 4 checked bags for 3 people! That's insane. Of course, we have 1 suitcase just with stuffed animals (what can I say, I'm a sucker). He bought them at DW over his lifetime and thinks they all need to visit their home. Cute, so I fell for it!
For clothing, I'm packing:
2 pr pants each (3 for me cause I'm special)
2 or 3 pr shorts each (I'm being optimistic)
light jackets that we'll wear from home
5 or 6 short sleeved shirts
2 or 3 long sleeved shirts (can be layered under or over short ones)
1 sweater each
Keens, flip flops and tennies for each (and Uggs for me)
gloves and hats just in case (and they don't take up any room)
bathing suits because we'll swim no matter what
cover ups and towels
I keep looking at the weather and hoping. We've been 2 other times in the winter and were fortunate enough to wear shorts every day.
Good luck getting it together!