I wonder how much, if any, hearing, and, indeed, using, swear words, can ever influence the actual character of a child? By 'character' I am thinking, disposition, attitude towards other people, ie kindness, empathy, sympathy, tolerance.
Has anyone seen the stage version of Billy Elliot? The script is full of 'fucks' and 'wankers'. Do we really think the saying of those words damages the young, and brilliant, cast members?
I don't think your grandchildren will be harmed by hearing these words. It's the actual attitude of the people around young children that influences their natures.