If the issues related to feelings of loss due to infertility aren't resolved, parents can end up feeling removed or even resentful toward their children. They may be unable to acknowledge that their children have birth parents. Or they may be unable to accept with grace the ways in which their children are different from them in temperament or appearance or ability. Some of these reactions are perfectly normal at times. However, as with most things, continued denial can result in an imbalance in the relationship.
Children are sensitive to their parents' emotions and thoughts, even if they are unspoken.
I don't think that resolving any loss ever means getting to a point where the loss doesn't exist or doesn't matter any more. That we have determined that to keep trying to have a birth child is not the important thing anymore. Our purpose is not fulfilled by means of continuing to try to get pregnant, since our purpose is to have children. Resolving that loss doesn't mean putting the picture behind you. It doesn't mean pretending like the loss never happened or that it doesn't matter.