So you're saying their kid will have Pink hair?
While they do take different approaches, a mechanic and a scientist can work out to be the same thing at times, in certain areas. You'd see those two get along far more than either do with a Sheriff like Caitlyn.
I don't ever see Vi and Jayce getting along, now they ain't hating each other, and might enjoy the company of the other, if it's ever around. They'd fit so well in a buddy cop movie, all three of them. But as they say, a good measure of friendship is how much you can insult each other without offending them. I mean, I say please and thank you to strangers, friends get a stern command followed by generic insults about their mothers/weight/and hair style.
It's only one kid, like hell they'd have two kids, or be an actual couple.