Swimming on your Period?

I just became the coach of my first swim team, and I, being a male, am having a hard time with the whole period thing. My girls are middle school level, and a little shy about the subject, as am I. Now, I know that you can swim on your period by using a tampon, but they cringed at the idea. However, on a 20 girl team, I've got as many as 6-7 girls sitting out daily because of it. I know that's far FAR too high. I'm about this close to going out and buying a box of tampons to shove in their face if they don't dress. So my questions are: How necessary is it that you wear a tampon? Is it an every day thing? are there times when it's worse than others? And, how can I easily make the lives of the swimmers who don't swim (and keep in mind it has to be for a group of 6-7 people) a living hell. I need a dry land work out that can be done on the pool deck that takes little effort to watch (so I can coach the other girls) and something they can't really slack off - I keep giving them push ups and they barely go down. I really can't think of anything outside of making the actual swim session fun, so if you guys have ideas on how to do that too it might work, too. It need to work on something important though.