So to just go over a few pointers and add a few more (and this is from the mom's perspective... Seeing as I am a mom myself and I think moms are the ones to organize the family for photography sessions 99% of the time anyway):
-Let your kids bring something that will make them happy and comfortable (especially if I have never met them before) like a favorite toy or snack. For little ones I love marshmallows because they don't turn your lips blue and they disappear faster than... say... a big 'ol graham cracker in their hand.
-Dress for the weather! I cannot stress this enough. As adults, we can "fake a smile" well enough when we have to, but if your kids are freezing it is really really really hard for them to be happy.
-Bring other props for them to interact with.
-Never threaten with negative consequences, instead go for positive reinforcement (and yes, even bribery!) but be sure they are old enough to understand that the positive consequence (whether it be a sucker you brought with (an awesome prop by the way!) or whatever else comes when we are all done with the shoot.
-This is one I have a hard time "correcting" during a shoot, and I know it is just pure habit to tell your kids to say "cheese" but please please please for your own photographic sake and mine try and break that habit now! Look at yourself in the mirror when you say the long "e" in cheese. Almost any other vowel would give you a lovely smile, but the "cheese" smile is just not the most flattering. It's a hard one to break in kids (and parents!) Instead of outright asking for a smile, try a joke you know they will laugh at, or with littler ones a good game of peek-a-boo behind my back can often bring out some great natural smiles.
-Prepare your husbands. Grumpy dads give the kids an excuse to be grumpy too. Yes dad, you will get to be in more than one picture, and yes dad, you do have to wear that outfit that your wife picked out, and yes dad, the shoot may last as long as an hour and a half (the horror!) but your cooperation is so key to the success of a family photo shoot! To all the dads out there... You are awesome. Thank you for understanding! ;-)
-I will put you in some more formal poses, but then I love to see interaction! I may just give you a prompt and go with it. I may ask you to do something again because it was really cute. Don't feel like you always have to be looking at the camera and holding a smile. You don't always have to hold still. Don't be afraid to just be you!
-Along with the threatening, please don't make me out to be a bad guy. Saying things like, "do this or Alea is going to be mad at you!" only make kids more scared of an already big scary camera in their face. I promise I am nice and sometimes rather goofy and I am not mad if things don't go perfectly. Trust me, I have kids. I totally understand if it's an off day. I understand spit-up and blow-outs and tantrums and being scared... If things are really just not working out we can reschedule. Really.