If a parent has_many children, The children can be set using
parent.children_ids =  which is very cool. If the parent is a new
record, nothing will happen until the parent is saved. If the parent
is an existing record, the children will be immediately updated
regardless of whether the parent has been modified or validated. In
fact, the parent model will have no indication that the children have
been modified at all.
Am I the only one that thinks this is odd behavior? It seems like
there should be a more consistent approach.