Family portrait sessions are sometimes the hardest ones to arrange - simply because we're so busy anymore that getting the family together is a great challenge! But one day those infants will be teenagers and one day those teenagers will be out of the home starting families of their own.
Because family is so important I'd encourage you to schedule one about every 2-3 years.
Your kids will "grow up" and dad's hairline is going - - gone! But in my portraits your family will always be together in a happy time.