I would be apprehensive to wear any new shoe if you are going down during colder months where your family is used to wearing tennis shoes, or boots and then switching to any kind of sandal, including croc's. That said, we always wear them to Disney during the summer months because our feet are used to them.
When we go in early May, I will probably bring croc's and sneakers. I will have DS start with socks/croc's and see how it goes.
The reasoning I have is that if they are used to wearing tennis shoes and socks at home for school and stuff, then you know they shouldn't bother their feet because they're used to them.
Good luck with your decision!