My wife is an impulsive buyer and spends a lot of money without thinking twice. Am afraid we are not saving enough. How do I explain her?

Tell your wife that the cost of living all over the world is getting higher and higher. Raising a child is super expensive and educating them all the way till university will cost even more. Saving money is imperative for your family's future. You can show her this article: https://en.wikipedia.org/wiki/Cost_of_raising_a_child