By Harry Rutter Paris Hilton took fans inside her son Phoenix’s lavish 1st birthday party, attended by stars including Kelly Osbourne and Rumer Willis. The 42-year-old socialite threw the “Sliving Under the Sea” themed bash for her little one shared with husband Carter Reum. Paris transformed her garden into an underwater-themed paradise, complete with a giant multi-coloured balloon wall. She shared a clip from the party, talking into the camera as she held Phoenix, whose actual birthday was January 16. “It’s Phoenix’s first birthday and we have a ‘Sliving Under the Sea’ theme. I’m so excited,…