Uranus Altair Phoenix Castor Galileo Watson and Inne Portia Ophelia Bianca Calypso Holmes were aerospace engineers that met in their second and first day (respectively) working for NASA. Shit happened, basically, and half a decade later, they were already married and expecting their child - wip. Said kid was welcomed to the world nine months later, follow by Pluto Orion Pollux Caelum Puck Watson about i/t later. The third kid was Titania Eris Galatea Aquila Nysa Watson, who was welcomed into the world a year later.
Pluto's sarcastic comments, even as he was growing up, became part of the daily routine of the household. There were loads of jokes, loads, about his namesake and the family's saying of "puck off" also was derived from himself. Some in the family would argue these comments originated as a way of defending himself against the continual battering of small planet related jokes, others argue that it was - and is - his way of getting back at his siblings.
Pluto's always been one to deviate from his family's norm, not really having the greatest interest in space. That's why, quite naturally, he tends to be less close to his family and has developed a solidarity nature, especially at home. It was during one of his 'I'm not related to you people' phases that he had his first magical experience. It was quite simple, the model of a spacecraft his father had spent ages making for him exploding without a known cause. Let's just say he was slightly freaked out.
Years passed with Pluto keeping his experience to himself as, being him, he was hyper aware of the judgement of others and didn't want to appear weird or abnormal. He managed to keep it to himself pretty well; playing the broken model as an accident and convincing himself he wasn't a freak. That was, until, his Hogwarts letter arrived and exposing him. The rest is, well, history.