If you're photographing a family with young children be prepared in advance. Camera on and ready to start snapping straight away. This allows you to not waste valuable time before the clients arrive and let the kids go. Have toys to entertain the kids, hopefully the parents will help with getting the attention of the children if you're just shooting them. If you're shooting the whole family an assistant can be a god send. Though a puppet can also help. Something that grabs the attention just for that split second you need. Be patient, some times you might have to re-book them due to the children not playing ball. This happens but don't get mad just get that booking for another time.
Make the shoots fun for all involved, make the parents feel comfortable. Be confident in what you are doing, joke with the parents or older children. If you're laughing they are smiling. Get those photos taken!!