Hello Gretch,

 I know it is difficult because you are caught in the middle of your mother and your son. The way you were parented is possibly not the same mode that you wish to employ on your son right now.  I hope that my answer will help you with compromise.

First, know that children at the age of three need to have a few more explanations that 'Don't touch and it is an Antique". They are concrete learners and simple explanations can be helpful but the terms used must be developmentally accurate.  Antique is not a word in most three year old's vocabulary.  OLD is much better but then a child may think that something that is OLD is not of value (such as an old and torn sock).  So, perhaps you can use terms such as "This was a gift,  Grandma has a special door that is very pretty and can break easily, etc."  These are words that most three year olds' comprehend and retain.  So, in essence your child has retained a lot of information, but at his level of understanding.  (If you want to introduce the word ANTIQUE you must associate it with another known concept, such as OLD.)

You may wish to explain to your child when you first arrive at Grandma's house that a few things can break easily and make Grandma sad.  Go around her house and use the words that are more pro-active such as "This couch and chair is good to touch,  These pillows are fine, You can play in this drawer with Tupperware because they won't break."  When you arrive at the breakables then say something like "Uh -Oh these are not good to touch.  They can break.  When something breaks it will make people sad.  Please, don't touch. "  

Now here is the important part.  When you spot your son playing with "child approved" materials then give him much praise and even a reward.  (Such as helping to "cook")

When your son goes towards the "no zone" , such as the antique door, gently remind him that this is a "no touch, easy to break" item.  The use of the phrase in sign language for "DON'T TOUCH" can be useful because it is similar to an umpire saying SAFE.  The visual and verbal cues should help to reinforce this preschooler about safety issues and make all happier.

As for your mother, perhaps she can have a toy box of novel items that are not from  your home available.  Thus, he will be happy to always visit Grandma and her box of fun toys (blocks, legos, books, small figurines that are safe for his age, etc.) that are special for only visits.  This box of toys also may decrease on negative behaviors.

Good luck!

Louise Masin Sattler, NCSP
Nationally Certified School Psychologist
Owner of Signing Families
http://www.SigningFamiles.com