I would also suggest allowing more than an hour for family photo shoots especially with toddlers, to get the very best images, some times it does take 40 minutes for a child to relax, it is like flicking a switch and then all is fine. There is nothing worse than red eyes and cheeks from rubbing the tears away, if they need a feed take a little rest, I double up as chief bottle warmer.
Parents as others have said are part of the battle especially when they start manhandling them into positions it rarely helps and makes me cringe I know hoe the child reacts to that form experience. Just let them have a little play with some toys, then remove them once happy. If they are scared as some are do a few with the parents included, nice candid shots, often parents say they don't want to be in the photos but love them and you will sell more.
Good luck