If it's a family/fun occasion then I agree with "less is more", take the 24-105 and maybe a fast prime (35 or 50mm).
Also enough memory cards and batteries. A small tripod (e.g. Slik Mini-Pro) could come in handy for group shots that you want to be in too, and a remote control.
I wouldn't buy anything new just for this trip, unless it fits your general shooting style.
Make sure to keep an eye or hand on your gear in crowds.