The sitting is a rather grand title for "taking the photographs".
Prior to meeting I like to agree with you what you are looking for in terms of ...
In order that the children feel relaxed, I like to find out what interests them - what hobbies, music, films, books etc. they enjoy - so that I am able to talk to them - keeping them engaged and hopefully happy about having their photograph taken.
Typically, the sitting would last around a couple of hours - although on occasion, weather and other factors might lead to a longer sitting. It's really whatever works best for you and your children.
Within two weeks of the sitting I will arrange to visit you in your home for the viewing.