Yes, you will need to sign a waiver on board. Doesn't sound like this will be an issue for you since the whole family is travelling, but word of caution: when I sailed alone with my 19yo daughter in January, they wouldn't permit me to sign the waiver because we have different last names and we didn't have her birth certificate to prove I was her mother. Even though we showed drivers licenses with the same permanent address and she looks like my clone, we couldn't get it done for her, which was frustrating.