Before he even does anything wrong, the kids in The Cat in the Hat Comes Back are convinced that the Cat is trouble. And we can't really blame them. After all, he did cause a huge stink back in the first installment. And it's true that he isn't the best house guest in town: he barges in without an invitation, proceeds to dirty up the whole place, and then brings all his friends over. But things aren't always what they seem, and in the end, the Cat turns out to be a helpful little sucker. Same goes for Little Cat Z, who also seems pretty useless at first; after all, he's so tiny you can't even see him. Bottom line: you never know who's going to save the day.
Q: Why don't the kids like the Cat in the Hat at first?
A: Remember The Cat in the Hat? This guy has caused some trouble for them in the past. It's an exercise in learning from your mistakes.
Q: Is the Cat in the Hat a big troublemaker?
A: Seems like it, doesn't it? But he makes up for it in the end.
Q: How do we even know if Little Cat Z exists?
A: Does it matter? His Voom does the trick either way.