It is a beautiful quilt and I'm glad you are taking the advise to hold back from a small child using it. I agree with your wife about being cautious. In today's world many people don't understand/or value the work put into hand making such an heirloom. They wash things too much(in old days quilts were not washed excessively) which wears out the item.
So the question becomes do you want this piece of history to survive into the far future or do you not care about that and just want someone to use and enjoy as they see fit. Your grandmother obviously felt it was to be treasured and so she only used on colder nights to preserve it for future generations.
Whoever ultimately receives this treasure needs to be told it's history and value(monetary and nostalgic) and hopefully they will use care with it.