C.,
I'm sorry. I swear that cleaning the house and making sure everything soft that can't be washed is in bags in the garage for a few weeks and the constant vacuuming, cleaning is worse than taking care of their heads.
As for their heads, the last time one of my daughters came home with lice, we could not get rid of it. The conventional shampoo and even the prescription wasn't working. I was at my wits end when my sister told me of reading about mayo working. At that point I would have tried anything because I was close to shaving her long hair.
I had good plastic wrap, store bought mayo, and a package of the thin plastic shower caps as well as a good thick heavy one, both from the dollar store.
I completely slathered her head in the mayo, aaaaaall the way to the roots to make sure that it was covering her scalp, because it smothers them and I was not giving them any air pockets. I wrapped her head good with the plastic wrap, then a thin cap, more plastic wrap making sure it covered forehead, neck, etc, then the heavy shower cap and more plastic wrap. I wanted to make sure it didn't slip off and get everywhere.
Her head weighed about twenty pounds lol, so we propped her on pillows in her bed, brought her sandwiches for lunch and dinner, drinks through a straw and put on many videos. I would definitely not go less than 8 hours. You want to make sure that it suffocates both the bugs and any nits. It's worth the time to make sure everything is taken care of.
I spent hundreds of dollars before I found that the above process for about 8 dollars took care of it. And without fear of poisoning my child, repeatedly.
The most important thing is to make sure that the house is thoroughly, thoroughly cleaned because thats where they'll come back from. Vacuum and wash like crazy and anything that you can't wash and dry in hot hot.. put into garbage bags and toss them into the basement or garage, not to be opened before three weeks.
Good luck and if you need anything or have any questions, I am at your service...
L.