Birthday party invitation dilemma?

Just be honest with the child's parent. Explain to her that you didn't realized the party was on Father's Day, and you want to spend the day together as a family. Planning a child's birthday on Father's Day, she must have realized that some won't show just because that. Don't stress about the situation because she will understand. I had planned my son's birthday on Mother's Day before, knowing it was risky for no shows.