First off, we have to deal with a parallel to John's idiocy of last year. As you will recall, he took Ted's self-deprecating description of his bachelor pad at face value because a literal-minded dolt like him wouldn't understand the need to underplay the good things in his life Ted has; this led him to the idiotic conclusion that an abandoned shanty was Ted's cottage. Upon discovery that he'd led them the wrong way, Elly, who also thought that they were in the right place, spent weeks not talking to John and getting angry at the children for
That's because they'd ended up having to share their beds with the children, John with Lizzie and Mike with Elly; instead of making the best of things, the Pattersons whined piteously about how haaaaard it was to have to deal with their children. Speaking of their refusal to deal with their children, their stupid inability to supervise them adequately led to their being embarrassed by preventable nonsense.
This, of course, leads us to the most annoying part of traveling with the children: the destination. Instead of taking them somewhere fun, they were going to see relatives and get yelled at for being bored by stories about times from before they were born. The end result is that the Pattersons come to the conclusion that children and vacations don't mix because they're too stupid to cope with them.