Rent, better to save up just in case you have to move over seas. 24-105/f L is best for that 1 lens. I'd get the 17-55f/2.8 only if the family is gonna be indoors mostly like eating, hotel, not because of low light or fast aperture, you cant back up when a a wall is in the way. If you are going to be outside most of the time, sight seeing, water park, family park, when you know you can back up, 24-105 should do the job of just that 1 lens kinda thing. Again rent it, to save that extra cash for a big move that might happen, and you'll know if you will want to buy it before/after the move.