I also am reluctant to call parents regarding children's hygiene issues. When I do make those calls I acknowledge to the parent that this is a sensitive topic. I also make sure the family has access to running water, washing machine etc. I recently spoke with a second grader about hygiene and she told me they don't have soap at their house.
When I speak to the parent, I do try to frame hygiene as an educational issue: other children don't want to sit by the child if she smells, it makes group projects difficult, the child may be teased, etc.
In the past, I have done a brief hygiene lesson for the fourth grade. I used a poem called "The Dirtiest Kid in the World" from this site: DirtyKid
Then we talked about what that kid could do to clean up his act. I also had a hidden word find puzzle with hygiene-related words and a hidden message with the left-over letters. The kids loved it and got a hygiene-related prize like a toothbrush or deodorant when they completed the puzzle. The benefit of group instruction is that an individual child is not singled out.