If the children feel guilty about their mother, they may be asking for these things to happen to them unconsciously.
I would try to find out about the bag. By rights it should belong to the children, shouldn't it? Ask the place where she was cremated if they know, or start asking relatives. The worst that could happen is they think you're weird or get annoyed.
The children will have to learn their own boundaries. I can recommend the Hematite essence from Alaskan Essences <http://www.alaskanessences.com/store/advanced_search_result.php?keywords=hematite&x=0&y=0
>, and White Yarrow essence <http://morningstar.netfirms.com/yarrows.html
EDIT: I'll add that even though they may not even be asking for these things unconsciously, they would then be allowing whatever other entity to do so. Perhaps a ceremony to honor the things in the bag?
I feel it may be a good idea to ask around what happens if such a bag is cremated or goes into the wrong hands. Don't be too shy to ask around. I personally don't know yet.