Because we live in Southwest Florida, our typical family portrait will be the grandparents, their kids and spouses and all their kids. Oftentimes this is the first time the entire family is together for many years so these portraits are extremely important.  Here are some tips: 1. Do the most important portrait first. It's best to catch kids off guard. Once they get used to you, they tune you out. 2. When posing large groups, put in the smallest children last. They don't last long! 3. We give a "lecture" before we even start each portrait session. a. Take hairbands off your wrists (why do so many women do that?) b. Spit gum out. c. Take all wallets and cell phones out of your pockets. d. Adults and older kids - sit and smile! DO NOT HELP ME WITH THE LITTLE KIDS! If you help, I'll get great pictures of the little ones and scary pictures of you (and I make a contorted face for emphasis and humor!). Please note that this is really difficult for the parents of the little ones. They want their kids to smile and look great so they have trouble not helping. e. Have a few good things for people to say that will make their mouths look good: Cheese, Money, Disney, YES, etc. f. The first time you ask the group to say MONEY, only a couple will. Encourage them all to -- this will help the little ones think this is something fun to do. Otherwise the little ones will only be thinking about how to escape. g. If there are extra people or you have an assistant, instruct them to stay directly behind you or out of sight. Nothing smacks of an unprofessional portrait as having everyone looking in different directions. You need all eyes on YOU! h. Mix it up. Say MONEY a few time, say CHEESE a few times, squeak a toy (directly above your head or lens) a few times. With little ones or pets, they tune out after about three.
One reason to have an assistant is to make sure necklaces are straight, hair all looks good, etc. They may see things that you don't.
Another reason is for candids. Everyone loves candids so the assistant can be shooting "between the shots" pictures. Your assistant can be photographing closeups of the faces of the little ones as they are running around in the background while you are photographing the smaller family groupings.
If you are a photographer who only shoots candids, please let your client know that ahead of time. You can't imagine how many reshoots I have done for clients disappointed by hiring a photojournalist instead of a portrait photographer. It's virtually impossible to get a large group of people to all look good in a candid situation.
Once we photograph the large group, we move on to the smaller family groupings. With four or five people, we can photograph those candid looking pictures that people love. We love to feel the love and connection between family members! 
You can have a lot more fun and be more creative with a family with all older members.  
Managing people is a huge part of a portrait and wedding photographer's job. It's a skill that is learned with education and practice.  | 
