“My in-laws spoil my children. The kids don’t close their mouths after talking about something they want and off go grandma and grandpa to buy it. I did not grow up this way and I don’t want it for my children. Please help.” (Email not gender specific)

Timing is everything...
Second: Speak up, and do so without alienating your in-laws. This requires great skill, an advanced sense of timing, and a great deal of poise on your part. Choose a time when anxiety is low – a time when you are all feeling good about life and each other.
Third: if you are successful, your in-laws will thank you for your insight and somewhat refrain from excessive shopping. You will need to remind them (playfully) of your chat several times over the course of a year.
Fourth: If you are unsuccessful, everyone will end up on bad terms, your in-laws won’t shop for the children again and your children and spouse will be as frustrated with you as you are with your in-laws.