Indeed these are the very things that nannies and other surrogate parents do, and we know that children can form strong attachments to these people. They are the glue that cements an attachment. The idea that a parent may get short-changed or penalized seems to me to reflect the idea that children are parental property, to be divided equally along with other assets. I would argue that co-parenting should be a goal that is achieved as soon as each parent is capable, but should not be taken for granted at the outset of a separation.