Andrea
That was definitely the one of the worst things I had to deal with as a parent! Two of my kids got it when I was pregnant with my third, and then I got it too. There is a book called "The Lice-Busters Handbook" which is worth getting as it has a lot of tips. You might want to try washing their hair with Prell Shampoo, then leaving on the Nix lice shampoo (unless there is a better one out now, this was 7 years ago for me, but the memories are still vivid) for ONE HOUR with a shower cap on their head. This finally did the trick for all of us when I was at my wits end with nits! GOOD LUCK.