K.K.
I have the same problem with my MIL. My twins are 3 and I tried to battle this for 2 years. Finally, I just let her buy them whatever she wants and then when she leaves town, I donate the clothes or toys (or replace some of their old toys with the new ones to cut down on the amount). She gives so much that she doesn't even remember what she has given. That way, she still has the joy of giving to her grandchildren and we have the joy of donating to children who really need the items. For their birthday this year we asked people to bring used/new books to the party instead of gifts. All of my friends did, but family didn't. I set up a time to take my kids to the Children's Hospital and they saw first hand where their books were going. I think it is a fabulous idea to teach this concept along with allowing them to receive gifts from grandma. Good luck! You'll feel like a full time toy/clothing manager!!