How would you deal with a friend's child breaking something costly in your house...

...and your friend did not offer to replace or repair it?

I would be really upset though I would probably not end up saying anything to them about being reimbursed. I would make a comment if the kid was ever around again to the effect of, "Replacing what he broke the last time set me back, so we need to watch him carefully today."

But if it was something huge, like the kid took something sharp to the tv, I would have to ask if they were going to help out with the cost.

The bitch will pay for it eventually. And I would be very vocal about it.

If it was especially expensive, they would have to pony up the cash to replace it; even if in installments.

Um. Depends on what happened. Sometimes accidents happen but if the kid was being careless it's kind of on me too to a certain extent for not stopping them from doing whatever they were doing to cause the damage. As I said. It depends.