The best advice I can share with other moms is this: Don't give in to guilt. Your kids won't love you less because you refused to buy them the latest video game. If anything, they'll love you more when they see you as the strong and financially capable woman who keeps a roof over their heads.
If by age 9, my daughter already has a Kindle Fire, access to an iPad and has been to New York City twice and on and on, what is left for her to experience when she is older? Am I somehow setting her up for crushing disappointment?
Your parents are not trying to undermine your goals. Just like you do, your in-laws want your children to become appreciative, and have "the right" values. But their desire to be adored, even favored, can trump their common sense and your goals.
Consider what today's parents face -- the corporate influence, billions of dollars of advertising, and a banking technology that has taught children that money doesn't grow on trees, it comes flying out of ATMs.