If one of my children has left college, do the payments stop?

hi im paying the csa for 2 children one is nearly 18 and the other is 16.the 18 year old was at college but now left so does it stop for them? also i had a baby with my new partner in july 2011 new do my payments go down because of a new child?.im also moving to maidstone and need to travel to work is that taken into consideration?