The dad’s brother paid for the Paris trip. He had been watching his niece (the older one that counts everyone) while he worked in Paris, and in exchange the brother paid for them to go to Paris for Christmas (and also no doubt so he could see his kids). The brother is loaded, as we also see in the second move, he is remodeling a New York brownstone in midtown.

That says, they do pretty well. It may even be the mom with money. There is evidence to suggest she is a fashion designer with all the mannequins in the house. But the following year when they pay their own way, they go to Florida and not Europe, so they are probably not as loaded as his brother.