What are the ages (generations) of the family? It is usually best to place the oldest (most revered) in the centre, then build the group aroound them.
Try to get some variation in heights, you do not want them all on the same plane.
Do not use too wide an AOV to try to get them all in, it will introduce unflattering distortions. For children under 2 years old it is best to get the parents to hold them.
If you have the room, leave a little room between your subjects and the wall to increase depth, but not at the expense of subject to camera distance.
If you do not have the room indoors, this type of group can be very successfully taken outside on an overcast day (diffused lighting). Finding a slight rise or steps with a nice background behind will aid your composition.
If the children are of an age that can converse, ensure you tell the adults NOT TO TELL THE CHILDREN TO SMILE, or talk to the children once they are in the group (as this will distract the children from you) ask the adults that once posed, they concentrate on looking in the direction of the camera which will allow you to talk to the children and try to elicit a smile though chatting with them about things they like, concentrate on the children as they will be the most difficult to control and let the adults look after themselves (within reason).
I would use an aperture around the f8 mark for a standard or short telephoto length to ensure that all the group are included in the DOF, but this will really depend on what focal length you end up using.
Hope this helps!