It's all part of Voldemort's plans, I'd wager. Don't imagine his Lordship would put the lad in a position where he might get too mangled, and aside from being convinced that he's the key to immortality, having a son makes him more relatable to his people.

He'd probably put his own name into that goblet, if he could, but figures this is the next best thing. Cos isn't it all a part of the same rabble, the Tri-wizard tournament and the Quidditch Cup? Voldemort's rolling out the red carpet to show off his creation.

Don't know what to say about the Malfoy lad. Always seemed he was raised up to be something of the prince's whipping boy, getting punished in Harry's place and such, the sort of thing a posh Malfoy ought to deeply resent. But suppose there could be a real bond there, too.