DEAR ABBY: You will be blessed from coast to coast if you publish this open letter to all grandmothers:

DEAR GRANDMOTHERS: Please don't play favorites. If you buy a gift for the children of your daughter, please buy a gift of equal value for the children of your son. These children are cousins, and cousins play together, and when they see the expensive toys, books and clothing that Grandma has given their cousins, they become jealous because Grandma has never given them such grand gifts. She gives them cheap little trinkets - or nothing at all.I am the mother of the cousins who get very little from Grandma, and I have looked into the sad eyes of my children when we visit their cousins who have been showered with expensive gifts from Grandma. It is always the daughter's children who are favored. I have friends who are in the same situation, so I am not imagining this.

I realize that there are some grandmothers who are fair to all their grandchildren, but I am sorry to say that they are the exception.

I hope that this letter will cause the grandmothers who are guilty of this kind of favoritism to change their ways. Most children don't "need" anything - but they are hurt when their cousins always get the peaches and they get the pits.

Thanks for listening. - YOUR SON'S WIFE

DEAR ABBY: We have a very kindly neighbor who makes jellies and jams all summer long and gives them out to everyone she knows. We appreciate her generosity; however, we do not eat her gifts because she doesn't can properly. She just cooks the fruit and puts it in any old glass jars she has around. She doesn't sterilize them - no seal, no waterbath, nothing. Of course, most of it is already spoiling by the time her neighbors get it.

Our concern is that she puts so much effort into it, we haven't the heart to tell her she might poison someone - much less tell a 60-year-old woman that she doesn't know how to can properly.

Please help us, as she is such a dear sweet friend. - ELSIE AND LOUISE (NOT OUR REAL NAMES)

DEAR ELSIE AND LOUISE: Can't you offer to "help" her can one day? Then introduce her to some "newfangled ideas" such as special jars, sterilized sealing, waterbath, etc.? You would be doing her an enormous favor and, who knows, you might even save a life!

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Abby's favorite recipes are going like hotcakes! Send your name and address, plus check or money order for $3.50 ($4 in Canada) to: Abby's Cookbooklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)