Father's Day is here! Stars across the country are celebrating the holiday with sweet posts and messages of love and appreciation.Some famous faces are celebrating the holiday for the first time as new dads, while others are commemorating the occasion by sharing pics of their adorable kids.ET is rounding up all the sweetest and most adorable posts to get in on this year's big Father's Day festivities.Katy Perry celebrated Orlando Bloom with a sweet video that appears to show him — decked out in