After you say "no"...completely stop playing and ignore her for a while. If you have to...leave the room. If you start playing with her right after you said no, you defeat your purpose.
I'm not crazy about the holding the mouth closed part, but that's me. You could also just say "no-bite" and then ignore her. It could help to define a difference in no's. I also wouldn't use tug toys with her until she's much older.
I do believe that establishing the mouth as a no play area as a young pup, helps to establish limits when she'll be older. Since you have young children, completely making hands off limits to mouth will be easier than trying to figure out either/or situations. I hope I"m making sense there. :D
good luck & enjoy your new baby
toodles